This error occurs when adding a theme:
Assertion: bit in range failed at line 286 of file "../base/bitmap.c"
The attribute table or INFO directory for the coverage is corrupt. For example, you have an ArcInfo coverage of zip codes, c:\gis\zip_workspace\zip_cov, that was added to a project. The attribute table was linked to another table and records were deleted while editing.
The error can be avoided again by deleting the ArcInfo workspace and reloading the data.