Are you sure that it is not a 9/065 error instead of a 9/064 error?
A 9/065 error is a locked file and this would occur if you are not opening the file in a sharable manner.
How is the file defined in the SELECT statement? Do you have a LOCK MODE clause defined as either AUTOMATIC or MANUAL? If you do not have a LOCK MODE clause then the file will be opened as exclusive which means it is not sharable.
Thanks.