Disable what AV software? Not sure what you mean by that. I can try using an older backup.
Hunting around Apple's support documtation, I found a few things to try. One recreates the iTunes library file from the XML file. I'm not sure what, if any, information will be lost (Apple does say that the XML file contains most, but not all, of the information that is in the actual iTunes library, but I'm not sure what exactly that means here).
Another thing I can try is to
Antivirus, assuming you have some... Various AV programs have been known to disrupt iTunes, and a library upgrade is one time when you really don't want that to happen.
Importing the XML file cannot restore the original date added values, not will it resore any data for files that aren't where they are expected to be...