We came to the conslusion that it's a bug within VFP 6. There is another field in the cursor with a similar name(part_num). There has been no recent upgrades to our LAN or OS's. We reworked the logic to use locate command instead of the seek command. There are less than 30 records in the cursor so performance is not an issue.

Thanks for the help

Jim
>I think your problem occurs before the indexing. "Cannot update cursor" is probably a response to your "INDEX ON cldpart_num TAG cldpartnum ADDITIVE" command, which fails for some reason. I expect that "Index tag not found" is a symptom of this failure, not a cause.
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>As for why a cursor created with "CREATE CURSOR" can't be updated, it could be system-related: out of disk space or memory, the OS has only allotted a certain amount of space in \Windows\Temp, etc. - this could explain why it came upon you suddenly. Sometimes an OS (especially Novell) marks files or directories read-only or unsharable. I'd look for any recent maintenance done on your LAN, OS upgrades, etc.