How have you stress tested your overclock? Your overclock may be stable at normal loads, but may have issues at high load or the system may have issues with proper cooling. Check your vents and fins for dust.
If none of that works and you want to see if it is a software issue try the latest BOINC program install. It is the underlying tech of Progress Thur Processors. It is not as refined as Progress Thru Processors, but will let you test to see if it is a software issue with the program or an issue with you computer or the overclock. If this does not work I would recommend just testing without the overclock and you can find if its the overclock or another issue.
I hope you find out whats the root cause as we would like to know if its the software and something we need to fix.
Good luck!
