If scan pst will not fix your issue the CRC errors are because there is a problem with the file itself. I would say the data in that file is gone. You could pay a data recovery company to dig through what you have and see what they could restore. I've never used an 3rd party product that could recover a PST from an error that scanpst could not also fix.

Teach your user how to backup as a restore is likely your only option. I would also check out the hardware for a failing diskdrive.

Oh.. I have several pst's that are over 1GB in size and I've never had any issue. You just have to manage them properly and watch the maximum size. Outlook 2003 can handle up to 18GB pst files. Pre-outlook2003 can only do up to 2GB.