Cryptographic service disappear on Win2k Server

I have a windows 2000 server with service pack 4 installed. When I try to
make the windows update it always give me the error 0x800A138F. I think
this problem was there before service pack 4. So I try many solution that
are on the www.updatexp.com site but nothing work.

But here is my obsevation: Cryptographic service disappear form the service
list and the file sccbase.dll disapear too. When I execute sfc /scannow
everything seem to be OK.

So how do I correct this problem? How do I get the sccbase.dll file? Is it
possible to uninstal and reinstall cryptographic service?

Dany