Yeah, unfortunately we cut it off at 5.2. I suppose it's possible to get it to work if you install the json extension (I don't think there's anything that woul

Yeah, unfortunately we cut it off at 5.2. I suppose it's possible to get it to work if you install the json extension (I don't think there's anything that would actively preclude it from working), but I can't make any promises because I can't get an isolated PHP 5.1 install to build in my dev environment (believe me, I tried, but it wasn't worth it). Let us know if you give it a shot and can get it to work, though!