SSL Certificate Installation

Can you check if they are indeed a pair,

openssl x509 -noout -modulus -in /path/to/certificate.crt | openssl md5

openssl rsa -noout -modulus -in /path/to/key.key | openssl md5

Looks like your certificate and key do not match. Follow jaikumar's steps and verify key/cert match. If md5 sum is not identical, contact your CA and get valid files.