There is a couple of differences:
The system where winbox is working ok: win 7 ultimate /32 bit - avira anitivirus
The system where winbox is very slow: win 7 Ultimate / 62 bit - avast internet security.
But as mentioned I have tried to disable the avast internet security, which did not help, and it did work in the initially. It some change in my system that has caused winbox to become very slow to detect units on the lan and also to time out when trying to connect to a mac.