Outlook does not decrypt incoming emails

Hello,

i got following problem:
 

We installed Symantec Encrytion Desktop. Everything works fine I can send and receive encrypted emails. The "only" problem is that Outlook 2013 does not decrypt the incoming emails. I only see lots of figures and letters like for example:

bp6SpWaeaSCzJNtIZy2rMb+8nyakTuchEgqyIXvctZ5d0N6eDTQlHDq6Ze1T

I have to move the incoming email into the PGP Viewer.

The weird thing is that it already worked some weeks ago but then suddenly it didnt work anymore. I changed nothing in Outllook oder Encryption Desktop.

Is there anything that i can check by myself to fix that problem?

Hope you can help me. If you speak german you can answer in german.

Thank you in advance