Client Authentication App can not validate Certificate (only with admin user)

I have the problem when a user is logging in at the Sophos Client Authentication App, he get's the failure message:
"Can not validate Certificate SAA will close now"

Wired thing is, when i start the App with Administrator privileges and the user logs into Client Authenticaton App with his own sophos credentials, it works fine!
(until the user reboots, the problem occurs again.) When the App is running it is working as expected and authenticates the user with utm rules.

Since it is a Domain Network i have to install the app (exe file) as Admin and i also tried to install it on C drive outside the standard AppData path.
I installed the App on user profile logged on and also when Admin logged on > same result.