I met the same problem while import the gerber file to CAM350 that is created by Boardstation , but i have not checked reason .
I need help for this action.
I had the same problem doing custom IDF's ( converting tracks and planes ) from BoardStation or Expedition to mechanical tools.
All the problem were due to rounding or precision on the MCAD tools. trying to close the polygon it would miss or overlap and generate the same
error message ( very small, 0.0001mm or more ). Changed the precison on the MCAD tools to be smaller when reading files and I think added a pass
on the IDF to search for x/y inferior to a certain distance between 2 successive lines and round them to the same point so it would be continuous.
And would check that first line and last line of the polygons were identical to close.
Not sure if it helps but might give you some pointers.
If you have access to the Smart Utilities tools in Expedition you can allways try the "Outline Optimizer" on polygons to fix these problems.
If you don't use the Smart Utilities tool, enter Draw Mode, turn snap on and "trace" over the offending polygon with the add polygon tool. Once properly established, delete the original polygon.