I Got the solution! TRUST ME!
Step 1:
go to settings --> General
scroll down all the way to RESET
Click it then chose --> Reset Network Settings
then click the thing in RED color (which means you confirmed it)
BE AWARE!!! if you do this you will have to re-enter your wifi password so make you remember it!
SO...
now iPad will restart
Step 2:
connect to wifi --> enter password
go to general and then software update and re-update!
congratulations! The process takes only 3 minutes without the need to go to an Apple Store!
this error happens usually when you have skipped an update!
enjoy!