The connection to the server was lost 'Periods Category' (OACP)

Dear Experts,

I am on a client machine which acts as a server as well.I create a an A/R invoice  and when i click on add it gives me an error 'The connection to the server was lost 'Periods Category' (OACP).

In addition when i run a query on the the OACP table it gives me the same error'The connection to the server was lost 'Periods Category' (OACP)'

The client is the same as the server.I have tried restarting the machine severally but without success.

My client is on SAP B1 version 9.0 pl 12

Attached see the error message .

any clues?