Is this a duplicated system? When you take that kind of a jump in software versions their is a lot of hardware that will need to be upgraded as well. My last upgrade was from v4 to v8. 2 extra memory boards were installed, the processors and optical disk drives. It took 3 different times to finally get the new software loaded. Bad boards were part of the problem. They missed another board that was to low a vintage and had to order 2 of them. Your system will not be very happy at first with new hardware installed that it doesn't reconize. Your vendor should have a cut sheet with the steps to do the upgrade. Ask them for a copy and look at the minimum vintages on your exsisting packs to make sure nothing has been left out. One other thing you may what to do is to look up the voice report @thevoicereport.com. They have done several articals on V11 software they may let you know about potential problems. If you find any mistakes, please consider that they are there for a purpose. And everyone needs a purpose.
Hope this helps, Mikey.