ACAD Map: Link Does Not Belong to Any Polygon?

I'm using Autodesk Map 2004 (but I also have ACAD Map 2006, so suggestions are welcome in either version! The process and error
message are the same regardless of which version I use) on Windows XP Professional x64 Edition OS.
On a seemingly random selection of drawings (though always on very large objects - hundreds of kilometers in length), I get the error message "link does not belong to any polygon" when attempting to create a topology. Even when I explode and rejoin the object the error remains (and always in the same place - the start/end point of the polygon?). Equally, when I trim or delete polylines around the error and draw new ones the error remains (though it moves to the end of the new polyline). When I divide the polygon into two or more smaller polygons I get the same error (which follows the original link around), even when it is no longer the largest polygon in the drawing.
The polygon is closed and can be hatched, but the topology function can't get passed the mysterious link. There are no other identified errors in the object, and the error has always suddenly arrived after all other highlighted errors have been corrected.
I have not deleted and redrawn the entire polygon because the area is far too large and intricate to be tackled, particularly as I don't know if it will solve the problem. If I knew for sure it would fix it, I would devote the 2 days necessary to doing it by hand.
Can anyone help me? Is this a x64 problem? I have had other unexplained problems which were solved by switching work stations. This one, however, doesn't seem to react to different operating systems.
Thank you!
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