[CentOS] SSL Library Error: -8181 Certificate has expired

Hi List
Just had one of my servers fail serving web pages and apache produced a 
log file of nearly 1,000,000 lines and 130Mb in about 18 hours with the 
following:
"SSL Library Error: -8181 Certificate has expired
Unable to verify certificate 'Server-Cert'. Add "NSSEnforceValidCerts 
off" to nss.conf so the server can start until the problem can be 
resolved."

repeated any where from 4 to 20 times per second until I stopped the server.

Anyone know why this kind of thing occurs - surely logging this once is 
enough??
If it is such a critical thing, then why no warning in the log files 
that it is about to expire??
- all in all a bit of a surprise.

The suggested remedy does work and I will get a new certificate issued 
and installed in due course.
Google does not show me anything that helps in regards to my questions.

Has anyone else seen and solved this in an elegant manner?
TIA
Rob