There are a lot of posts about XP issues in the forum, so Kristen'answer may help you. In my opinion, OpenCL 1.2 is not supported in XP, but for OpenCL 1.1 I'm not sure. So you should try it , use 1.1 or 1.0. Second, you should install an old driver. Third, -49 means that the arg index is invalid, so you should check the arguments of your kernel and clKernelArg().