error message in form

[Achieva]

I have a form based on a table with a subform based on a query.

When I go past the last record to a new blank record and then go back to the
previous record ... I get the following error message:

"You tried to lock table '~sq_corderssubform2~sq_ccustomerssubform1' while
opening it, but the table can't be locked because it is currently in use.
Wait a minute , then try the operation again."

I am not trying to lock any table, and I am uncertain as to what is causing
the error message.

Any answers appreciated.