How can I restore my iPad from iOS 5 to iOS 4? I updated my iPad from iOS 4 to iOS 5 yesterday, without making any backup. However, I  found that it is not convenient for me to debug my programs. So I want to restore it to iOS 4 again. 

I did as follows:


Downloaded iOS 4.3.3
Downloaded iTunes 10.4 to replace 10.5
Connected iPad with my PC
First, I click the on/off button for seconds and then keep clicking the on/off button and home button for about 10 seconds. At last, I keep clicking the home button only for about 15 seconds. iTunes detected my iPad in restore mode.
Following the tips of iTunes, I clicked "Option" and "Restore" button to choose the Firmware I downloaded and tried to restore my iPad.


However, something is wrong here. The error is:


  this device isn't eligible for the requested build


Can anyone give me an idea?
iTunes will not willingly load a lower iOS onto a device. Have you looked into the tiny umbrella program to see alternate methods to trick iTunes into doing what you wish. 

iOS 4 requires an shsh key to sign the 4.3.3 package for your specific device. This key normally comes from the itunes actication servers. Unless you have already saved that key, the automation tools won't work and you'll have to do muh deeper hacking to crack this nut. 



tl;dr 


read up on jail breaking
it might be too late for you to go back easily