What do you mean when you say it doesn't work? Did the app get installed but it can't be launched? If so, the most likely cause is that your iPad's device ID (UDID) is not added to the mobile provision file that was used to sign the app. iOS app fails to load on iPad or iPhone
After you added the UDID, did you then edit the mobile provision file, download it, and use that mobile provision file to build the app? In some cases, people will add the UDID and then fail to include it in the mobile provision file or use the old mobile provision file.
You might also want to double-check your UDID, especially if you used a third-party tool to obtain it. Use iTunes or Xcode, and copy the UDID, not the serial number.
It could also be a mismatch between the mobile provision file and the .p12 certificate you used. You need to use the same p12 certificate you selected when building the mobile provision file.