>This is almost always a blown .cdx file. try deleting the .cdx file and recreating it from scratch. It is sometimes more esoteric problems (like with video cards or printer drivers.) Start with recreating the .cdx and see if the problem goes away.
>
>Remember, the best way to reindex is to delete all the tags and then re-issue the index on commands to build them!
>

It also occurs in a blown memo field, and can occur if the related "memo" field of some VFP thing like a project, form, report or VCX gets corrupted.