error causing MTA to terminate

I have NT 4.0 and I am having problems with Exchange 5.5. Dr Watson pop up says application error occurred. EMSMTA.exe Exception: illegal instruction (0xc000001d),Address 0x00406630. MS message transfer agent stops but I can manually start it. The event log says, event ID9405, error, MSexchangeMTA, Category: Field Engineering. Description-Unexpected error may cause MTA to terminate. Error:access violation(0xc0000005 at address0x415f4 reading from 0x2d303538(BASE APPLICATION 39)(16)
We have been having problems and restored exchange data and logs from backup. Ran a 1 1/2 days fine and now this..