I downloaded the latest nightly build to test a fix that Matthew pushed. That fix (a refresh problem) worked, but when I tried to run some numerically intensive things - like the test for the science collection - I ran into problems. The science test hangs on the last differential equation test - eventually it runs out of memory. Some other examples seg fault in the garbage collector. I tried both 32 and 64 bit windows versions and they both had the same symptoms. These all work fine in 5.1.2. I tried a nightly build from yesterday (5.1.2.4) and one from this morning (5.1.3.1) and they both had the problem. Sorry I can't be more specific. You can require the science collection from PLaneT - williams/science/science - and run science.test.ss. That one fails every time for me by running out of memory eventually - I typically have memory limited to 4096MB on a 64-bit build or 2048 on a 32-bit build. I also tried some of the simulation examples that use the same differential equation solver - they're in williams/simulation/simulation. For example, model-2a.ss will sometime run fine and sometimes fail with a seg fault. Another one that fails sometimes and runs others is interactions.ss in the simulation collection. Let me know if I can get you any other information on the problem. Doug