ResolutionFind the proper key and certificate pair. This can be done by using OpenSSL to check the MD5 hash of the key and cert. If the MD5 hashes of the key and certificate match, then they are a working pair. If they do not match, then they are not. Below are the commands to get MD5 hashes using OpenSSL.
openssl x509 -noout -modulus -in "C:\Some\Path\Certificate.crt" | openssl md5
openssl rsa -noout -modulus -in "C:\Some\Path\PrivateKey.key" | openssl md5
openssl req -noout -modulus -in "C:\Some\Path\CSR.csr" | openssl md5
You can use an online utility, like the one found at, for example, Certificate Key Matcher.
WARNING: For very high security environments, it is recommended to use OpenSSL to check the key and certificate locally.