Handshake error when receiving files from partner

Hi everybody,

When my partner tries to send me a file, I can't receive it because of a handshake error. In the status bar of the Mendelson OFTP2 software, I'm getting this warning: "No key found in SSL keystore".

Due to this error, I have to send a blank file to my partner to force the software to get the file that wasn't be able to trasmit to me.

In the warn message and in the System event logger, I get this explanation:

No key was found in the SSL/TLS keystore of your system.
You can recognize the key by the key symbol in front of it when you open the certificate administration.
Exactly one key is required in the SSL/TLS keystore to execute the handshake process of the line backup.
Without this key, you will not be able to make or receive secure connections.

I have my partner's certificate and mine installed in the software and all the trust chain validation seems to be fine.

Does anyone know how to fix this issue?

Thank you very much.