There are two reasons for this error message:

• When downloading YASARA, you selected a different CPU than the one in your computer. Go to www.yasara.org/update, input the serial number that is listed in our mail with the initial download link, and choose 'Many different, I want to install on multiple PCs' as your CPU.

• When downloading YASARA, you did not select a specific CPU. In this case, the processor in your PC is either many many years too old for molecular modeling (Pentium MMX, Pentium II, AMD K6 etc.) or a rather exotic model that is incompatible with the current mainstream CPUs. You can unfortunately not run YASARA on this PC.