I had this error when I tried to install an SSL certificate a client gave me:

[Thu Aug 12 17:30:37 2010] [error] Unable to configure RSA server private key
[Thu Aug 12 17:30:37 2010] [error] SSL Library Error: 185073780 error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch

The reason for this was me that was brain dead. But I am posting this so that you can see how to compare the .crt file and the corresponding .key file:

Server Certificate:

openssl x509 -noout -text -in certfile -modulus

Key File:

openssl rsa -noout -text -in keyfile -modulus

Compare the modules of the two keys - they need to match.