report can error when trying to calculate the distance to nodes

I got an Astrolabe error message when I clicked on the Gatherer icon on the mini map.

Message: Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:171: attempt to get length of field '?' (a number value)
Time: 12/05/10 23:02:02
Count: 1
Stack: [C]: ?
Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:171: in function `ComputeDistance'
Interface\AddOns\Gatherer\GatherReport.lua:517: in function `UpdateResults'
Interface\AddOns\Gatherer\GatherReport.lua:242: in function <Interface\AddOns\Gatherer\GatherReport.lua:241>
[C]: in function `Show'
Interface\AddOns\Gatherer\GatherReport.lua:496: in function `UpdateResults'
Interface\AddOns\Gatherer\GatherReport.lua:641: in function `UpdateDisplay'
Interface\AddOns\Gatherer\GatherReport.lua:659: in function `UpdateHandler'
Interface\AddOns\Gatherer\GatherReport.lua:113: in function <Interface\AddOns\Gatherer\GatherReport.lua:113>

Locals: self = <table> {
IconsOnEdge_GroupChangeCallbacks = <table> {
}
CalculateMinimapIconPositions = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:799
AllWorldMapsHidden = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:998
RemoveIconFromMinimap = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:551
GetDistanceToIcon = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:825
PlaceIconOnMinimap = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:483
OnUpdate = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:951
ComputeDistance = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:156
IconsOnEdge = <table> {
}
OnShow = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:963
GetUnitPosition = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:307
GetDirectionToIcon = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:836
IconsOnEdgeChanged = false
PlaceIconOnWorldMap = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:875
GetNumFloors = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:360
GetMapInfo = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:367
Register_OnEdgeChanged_Callback = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:848
UpdateMinimapIconPositions = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:703
GetCurrentPlayerPosition = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:345
MinimapIconCount = 0
ForceNextUpdate = false
WorldMapVisible = false
minimapOutside = true
ContinentList = <table> {
}
MinimapUpdateMultiplier = 1
OnHide = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:991
MinimapIcons = <table> {
}
HarvestedMapData = <table> {
}
OnEvent = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:905
GetMapID = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:349
processingFrame = <unnamed> {
}
TranslateWorldMapPosition = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:227
RemoveAllMinimapIcons = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:571
LastPlayerPosition = <table> {
}
IsIconOnEdge = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:832
DumpNewIconsCache = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:859
GetVersion = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:55
}
m1 = 475
f1 = 0
x1 = 0.44062773883343
y1 = 0.66663211584091
m2 = nil
f2 = nil
x2 = nil
y2 = nil
(*temporary) = <function> defined =[C]:-1
(*temporary) = 0
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to get length of field '?' (a number value)"
min = <function> defined =[C]:-1
WorldMapSize = <table> {
4 = <table> {
Message: Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:171: attempt to get length of field '?' (a number value)
Time: 12/05/10 23:02:02
Count: 1
Stack: [C]: ?
Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:171: in function `ComputeDistance'
Interface\AddOns\Gatherer\GatherReport.lua:517: in function `UpdateResults'
Interface\AddOns\Gatherer\GatherReport.lua:641: in function `UpdateDisplay'
Interface\AddOns\Gatherer\GatherReport.lua:659: in function `UpdateHandler'
Interface\AddOns\Gatherer\GatherReport.lua:113: in function <Interface\AddOns\Gatherer\GatherReport.lua:113>

Locals: self = <table> {
IconsOnEdge_GroupChangeCallbacks = <table> {
}
CalculateMinimapIconPositions = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:799
AllWorldMapsHidden = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:998
RemoveIconFromMinimap = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:551
GetDistanceToIcon = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:825
PlaceIconOnMinimap = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:483
OnUpdate = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:951
ComputeDistance = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:156
IconsOnEdge = <table> {
}
OnShow = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:963
GetUnitPosition = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:307
GetDirectionToIcon = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:836
IconsOnEdgeChanged = false
PlaceIconOnWorldMap = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:875
GetNumFloors = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:360
GetMapInfo = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:367
Register_OnEdgeChanged_Callback = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:848
UpdateMinimapIconPositions = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:703
GetCurrentPlayerPosition = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:345
MinimapIconCount = 0
ForceNextUpdate = false
WorldMapVisible = false
minimapOutside = true
ContinentList = <table> {
}
MinimapUpdateMultiplier = 1
OnHide = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:991
MinimapIcons = <table> {
}
HarvestedMapData = <table> {
}
OnEvent = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:905
GetMapID = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:349
processingFrame = <unnamed> {
}
TranslateWorldMapPosition = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:227
RemoveAllMinimapIcons = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:571
LastPlayerPosition = <table> {
}
IsIconOnEdge = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:832
DumpNewIconsCache = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:859
GetVersion = <function> defined @Interface\AddOns\Gatherer\Astrolabe\Astrolabe.lua:55
}
m1 = 475
f1 = 0
x1 = 0.44062773883343
y1 = 0.66663211584091
m2 = nil
f2 = nil
x2 = nil
y2 = nil
(*temporary) = <function> defined =[C]:-1
(*temporary) = 0
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to get length of field '?' (a number value)"
min = <function> defined =[C]:-1
WorldMapSize = <table> {
4 = <table> {
}
9 = <table> {
}
11 = <table> {
}
13 = <table> {
}
14 = <table> {
}
16 = <table> {
}
17 = <table> {
}
19 = <table> {
}
20 = <table> {
}
21 = <table> {
}
22 = <table> {
}
23 = <table> {