i get an error flag everytime i try to upgrade my ipad to OS 5.1? why?

What error? What does it say?

You can only upgrade to 5.1 direct from the iPad if you have iOS 5 or later. Anything less and you must do it through iTunes on a computer.

See iOS: How to update your iPhone, iPad, or iPod touch

http://support.apple.com/kb/HT4623

If you are currently running an iOS lower than 5.0, connect to your computer & click on the "Update your device using iTunes".

Try this - Disable your firewall and anitvirus software temporarily. Then download and install the iOS update. After you update to iOS 5.x, the next update can be installed via wifi (i.e., not connected to your computer).

 Cheers, Tom 😉