I just jail broke my iPhone 4 with 0.9.9b7 on iOS 5. It worked for about 30 minutes then went into safe mode and I tried to reboot 3 or 4 and it would not come out of safe mode. Any ideas on what I did wrong?
It means you have installed a Cydia tweak which is not compatible with your phone or iOS version.
Remove the last thing you installed or updated from Cydia.