I got this error message when trying to cut a polygon "The Cut Polygons task could not be completed. An Unknown error has occurred". Using 10.0 SP4. I zoomed out a little more, and cut the polygon in a different placed, and it worked. Even better, it got rid of the topology error I was trying to fix. The topology error was rather strange. It got picked up as a gap, but when I created a feature from it it had a value of "0" for the shape properties. I did a check geometry, then a repair, but those Null areas remained. We are having network issues and I was getting other oddball error messages with topology, so I copied the FGDB to the harddrive, but not seeing much improvement in fixing/finding errors. The area I am working on is quite large with a wide range of shapes& sizes of polygons.