Record Entry in Access 2000

The Order Entry System (Access 2000 Front end on 4 PCs, Back End on Server) has started to behave erratically. I have several menu pages (as unbound forms) used to navigate thru Order Entry, Product Updates, Invoicing, etc.) It has worked without any major problems for some time. That is until recently.

The difficulty is that the following is erratic. I can see no obvious sequence. Sometimes I can open the program to the Main Menu, select Order Entry Page, Select a specific kind of Order, and all works well. The new order is entered, printed, and additional orders can be entered. Or..., after some number (generally >5), after clicking the New Order Entry command button, I get the "The _____ command is not available now". It's not just this form, the same behavior can occur with literally any form. I have tried changing various vba commands from DoCmd.Runcommand series to doCmd.GoToRecord,, NewRecord, without success. I have closed the program, exited to the deskTop and still get the same error. If I go to the Forms page and open the form manually, it will generally work (but not always). It may be that it is somewhere in the save command, as I have a "Find" command button that is not visible during data entry; so, I tried moving from the current record by closing the order or invoice just entered and opening another form with another record source, closing that form and reopening the Order form again). No success. I have copied all the forms, queries, etc, into a new database without success. I have removed all Me.Allow statements and all forms are set to Allow = Yes with Data Entry to No.

Any suggestions on where to look for the source of the problem?

Thanks
Any suggestions