I just found the answer to my question in the MSKB (article #Q165068) and thought I'd post it here just in case someone cares.

The article states that variable length index keys are not supported in VFP5. My client has a table that he created with an index tag called State, which has the following index expression:

ALLTRIM(SUBSTR(AREA,AT(",",ALLTRIM(AREA))+1))

The table isn't exactly normalized and the field should be broken up into two separate fields but at this point he refuses because he has created reports based on that field. Anyway the article above suggests that you pad the expression with blanks to make it a standard length. seeya.