Can't sync apps

[spazoid121]

This might sound strange, but I just got a new computer and I downloaded my previous app purchases. It was quite a lot. I then updated my Ipad to the new iOS 5. When I did that it erased all my apps. I then went into itunes and tried to sync my ipad with my apps in my itunes acct. This is when it got strange, I couldn't check the sync apps box under the ipad. I could check everything else, contacts, calender, music, etc... but I couldn't check the sync apps box. I then tried to sync it with my old lap top and the same thing happened. Can someone please help me? This is very frustrating! Thanks