Certificate server will not issue certs. CSP Unavailable

I have a certifictae server that WAS working perfectly. The only changes i'm
aware of in the intervening period are

1) Manually republishing of root server's CRL to the location specified in
the CDP extension

2) Installation of MOM advanced client

The web interface reports "An unexpected error has occurred: The
certification authority has not been started."

This is incorrect, both "Certificate Services" and "Cryptographic Services"
are started.

The event log shows 2 errors

Event Type: Error
Event Source: CertSvc
Event Category: None
Event ID: 87
Date: 02/04/2008
Time: 14:22:42
User: N/A
Computer: SERVERNAME
Description:
Certificate Services could not use the default provider for encryption keys.
Keyset does not exist 0x80090016 (-2146893802)


AND


Event Type: Warning
Event Source: CertSvc
Event Category: None
Event ID: 86
Date: 02/04/2008
Time: 14:22:42
User: N/A
Computer: SERVERNAME
Description:
Certificate Services could not use the provider specified in the registry
for encryption keys. Keyset does not exist 0x80090016 (-2146893802)

The server has been rebooted. I've looked through KB & google and can't see
anything that directly relates. Bit flummoxed really.

There's one DCOM error in the system log, but I've traced that back to SMS

Hope you can help