The KPF4GUI.EXE error is a documented issue, we have had quite a few customers send in logs regarding the issue, and currently development is looking through them to determine a cause, and a solution. I cannot tell you for sure if this problem is going to be resolved via a patch in the near future or if is going to have to wait for the next build of Kerio.
As far as the BSOD issue, which has been mentioned earlier in this thread, this issue has been resolved in the most recent release (build 4.3.246), and was actually a problem in Kerio's original code.
I realize that the GUI issue is a nuisance, however this problem in no way impairs the programs functionality, nor does it cause any harm to the users system. I just wanted to touch base with you all and let you know that we are working on the issue.
Warm Regards,