Windows softphone not working, only CTI mode

[MichaelRS]

We are using 3cx in the latest version. Now some users reported an issue with their softphones. If they switch from CTI (which is working in coop. w/ the windows client) to softphone, they can't make any outgoing calls. The client shows "call error". I tried reinstalling the client, reinstalling the C++ redistributables, setting up a new account, I even installed the 3cx client on a "fresh" computer to make sure there is no old piece of data blocking the program. Any hints? Anybody else experiencing the same problem?