I have not been able to backup my catalog in Lightroom 4 since upgrading two days ago. I did not have this problem with 4 beta. It runs through checking integrity, backing up, and optimizing, and then I get a message that it was unsuccessful and to make sure I have enough space and check directory permissions. There is plenty of space, and I have tried to create it to two different drives without success.
I am using the 32-bit version with Windows 7. The size of my catalog is 1.7 GB and includes my previous LR3 and LR4 beta catalogs. Thanks.