I've tried the software as well and I've spoofed the Mac address of my phone and I've encountered the same errors. Simply retry until the software works correctly and that's it. Eventually it should work. I believe this is an issue with the software itself and the commands that it send to the Android operating system.
If you want, go to Settings > Applications > All and locate the app that changes the Mac. Tap on Clear Data and Clear cache, then start it and configure the necessary parameters.