Bookmark error when filtering Access table

I have a Delphi 5 application that uses ADO and access tables.
I have a client that is getting the error "Not a valid Bookmark" when I try
and perform a filter on the table. I am not using any bookmark, not
intentionally anyway. This error does not occur evertime, and I can not
seem to narrow down any unique circumstances when it does occur.

I am using :
cursorlocation : cluseclient
cursortype : ctkeyset
I set :
commandtext = select * from tablename where fld1="blablabla" and fld2 =
commandtype = cmdtext
Then I call :

Again this error does not happen all the time.
Any help would be greatly appreciated!

Thanks, Joe