Thanks all for your help
I've finally found the guilty service.
It was pcmonitor a remote monitor/control software. Once I've stopped it's service vmware converter could get the capacity of the physical drives.
It's rather curious because I've done several P2V conversions of servers using this software (so far the last one was two weeks ago - the difference between that server and this one was that the former wasn't a DC).
Hope this thread will help others in the future.