Please forgive me if you received this message twice. I believe that my first attempt to send it was swallowed due to my not being a subscriber to the list at that time. We now have a Windows server with 23 GB of memory temporarily available this week to work on this GHC crash. Is there anyone interested in having a look at the problem? Quick review: We have a proprietary app which crashes on Windows with a BEX64 error when it processes input data that causes it to use more than about 4 GB of RAM. The same program when processing the same data runs to successful completion on Linux. Jason offered evidence that perhaps this is a general problem with the RTS on Windows when more than 4 GB of RAM is consumed. Further information: We are using 7.6.2 64-bit on Windows, and 7.4.2 (Haskell Platform) on Linux. Our program also requires quite a bit of stack when processing that large data. I give it 128 MB. I just tried reproducing this problem by running a simple program that eats up lots of memory. First I used a list, then I tried "chopping things up" more by using a rose tree. In both cases, I also tried creating an intentional memory leak to eat up lots of stack. None of that succeeded in reproducing the crash. I wouldn't eliminate Jason's hypothesis just yet, but so far it looks like it's not quite that simple. Any ideas? Thanks, Yitz