VERY limited compatibility - or just having bad luck?

I ordered (AMD Duron processor) two modules to upgrade an older PC. Both modules were not usable effectively in this system. The first module was already immediately after installation in the memory test as defective on the second module after a few hours operation by application crashes and ultimately a Windows crash.

The modules have been reclaimed and returned accordingly. Have instead now two modules built by CM3 (www.Amazon.com/gp/product/B00196HLC4/ref=cm_cr_ryp_prd_ttl_sol_6) and for weeks no problems.

Whether this is rather an incompatibility or whether more of a fundamental error in the modules is not existed to determine with reasonable effort.