accounts service issues since V28 upgrade

SOLVED

i upgraded to V28 today, the server programme as well as all PC's.  Since then, each time i change company or someone comes out of sage and tries to login in again we get this message. The  service is running on the server, users are in Sage and working ok, its only when trying to access a second time.  fixing seems to be resolved by running the install programme again on the PC and using the repair option, restart and then login ok.   

any ideas please