I see no screenshots, but a bug is always possible - however in this case you probably had to ask Bill Gates to fix it. Memory allocation is done by Windows, not by Zorro.

There's also another possibility: Memory is still free, but not contiguous, so huge arrays can not be allocated. That's the reason for the 1200 MB allocation limit. The limit can be smaller when your memory is heavily fragmented. I have not experienced any problems so far with large tick data files, but maybe I was just lucky.