I have recently switched from Virtual Box to VMWare Player for running several system on my home server. The issue I have is when running 3 virtual systems at once, when I return to my computer one of them (not always the same one) will have shutdown after starting and running for a period without issue.
I am running Ubuntu 12.04 as host and 3 instances of VMWare Player. Two instances run Ubunutu 12.04 as a Cloud and Test system while the third runs Ubunutu Server 12.04 as a local Samba server. Each system runs 512MB memory on a 2GB host.
Only thing I can think of is not enough memory for the host, but I would imagine the system wouldn't boot if this was the case. I really haven't done enough work with VMWare Player to know at this point and I can't find anything related on the internet.