This indicates that our activation manager (melabsreg.exe) is unable to write to the registry on the computer. The activation process seems to work, but the activation data is not being recorded successfully. This can be due to anti-virus software, registry-protection software, modified access rights, or simply a corruption of the registry itself.
Try temporarily disabling any anti-virus or security software.
Some users have reported that starting Windows in "Diagnostic Mode" will allow the activation to complete.
Also try at least one cycle of uninstall/reinstall for PBP.