>Did You open the table with some IDX index that has name equal to TAG name?
>Here what HELP say:
>

>cTagName
>   Specifies a tag of a .cdx file that is used to search for the index key.
>   The tag name can be from a structural .cdx  file or any open independent .cdx file.
>
>   Note   The .idx file takes precedence if duplicate .idx file and tag names exist.
>

The table has a CDX. I never create idx indexs for my tables. Even if they are temp tables I still create the CDX indexs for them. I did find in the help that states

You can use SEEK( ) only with a table with an index order set, and you can search only for an index key.

I think they are saying that you should have an tag set on your table before you issue the seek. So if I never set an order that maybe the SEEK function won't work. That would explain why sometimes with no order set I get an error. But it doesn't explain why my seek if failing because the table does have an order set just not the one I'm seeking on.