Part of the problem may be the IT policy restrictions and they need to be removed. the errors your seeing indicate the OS is not on the phone. the other error ( 561 ) indicates an application push from the server failed. that could mean the IT policy caused this.
the other issue you may have is the OS your loading may not be for the model you have. It must be for the 8520.
Another problem is the phone may be locked to a specific carrier. Unless you get the codes and follow the process to "unlock" the phone you must use the OS from the carrier. Go to O2 and download their OS for the phone model
Good luck
Read the links attached and see if they help
Error "507" is displayed on the BlackBerry smartphone running BlackBerry OS version 7.1 and earlier
http://www.blackberryforums.com/rim-...ve-policy.html