Exhange 2k service unstaibility

Dear All, Our organaization is using Exchange 2k as a mail server, just yesterday I have done the following:
1-Installing exchange SP2
2-Adding the Certificate service to the Windows 2K Advanced server.
After that I got the following problem which is: the service called “Microsoft Exchange Information Store” stops itself every approximatly 15 minutes. I uninstalled the certificate and restarted the server, but the problem still exist. Any help

Regards,

Ammer Alselham.