2GB virtual Win7. But, it's not memory exhaustion, I fired up Task manager as soon as I got the first freeze, and later confirmed that memory usage never goes above 600MB, with 2 instances running. Scripts that I ran are Z1fx & Z2fx, I believe that I tried both combinations (aka Z1fx Trading, Z2fx Test and vice versa) and in both cases I finished with one Zorro frozen (the one that run WFA).

No extra messages, the window just freezes in the middle of the WFA run, it has "WFA Zorro... (Not Resp...)" in title, and when I try to close it, Windows popup comes up telling me that application is not responding, offering to kill it. Also it is not CPU bound when frozen, just plain not responding...

Just to make it clear, this is not a showstopper for me, I'll run WFA in another VM, no problem. I reported this just so that you know there's something fishy goin' on when running 2 instances.