Mihhael, Check you operator console for messages like 90% paging space in use and then 100% paging space in use. You can check with "Q ALLOC PAGE" what the current usage is. But you mention crashing your VM when you start a new WAS server, it could be that you then use more virtual storage than is available on the system and/or backed by paging dasd. I would allocate a few additional paging volumes and/or try to reduce the size of my virtual machines.
Ronald van der Laan
