efs key lost after adding computer to essentials 2012?

Hi,

I added a computer with the "Computer Connect" Tool (from http://server/connect) to an essentials 2012 server.

Some of my files were encrypted with the efs and now I cannot access them.

There is a certificate under "certificates (current user)/own certificates/certificates" (which has a private key) that could be the original efs certificate (according to the creation timestamp) - but I cannot access my files.

How do I get the original key (if the Backup is corrupt...)? How can I access my files?

Thanks!

   Stefan