Error 1015 when restoring iPad

[gerjana]

My iPad is in recovery mode and needs to be restored. Error 1015 comes up during the ' restoring iPad firmware' stage.

I have already tried the following without success:
- downloaded latest version of iTunes
- made sure my operating system is up to date
- restart computer
- disabled Internet security protection
- created a new user on my PC and retried restore
- used another computer

Please advise what else I can do to solve Error 1015