I see many people with this problem, They update to the latest iOS version and jailbreak tethered. Problem is many people have compatibility issues with apps and therefore they don't function properly. This is a tutorial on how to change your firmware from 5.1 to 5.0.1
1. Go to /var/System/Library/CoreServices and then scroll down to SystemVersion.plist Open that up and you will see some code in there. Here's what you need to change:
If this does not work, it isn't compatible with 5.1, It should work with most apps though including Cydia tweak and App Store apps.
<string>9A405</string> <--- Yours will say something else, change it to 9A405.
There will be more code here (It's not important. This next part is)
<string>5.0.1</string> <--- Yours will say 5.1 change it to 5.0.1