Error: Unable to Save Edits
This problem is addressed in ArcGIS 8.1 Service Pack 1. See Related Information section to download this pack.
ArcMap may return ths error when trying to save edits to a polygon coverage:
Unable to Save Edits
When trying to save coverage edits, arc features with exactly 500 points are not handled correctly.
Solution or Workaround
Identify features that contain 500 vertices, and split them prior to saving edits.