Unknown Error Occurred (-54) Enabling iTunes Match-Collection of common programming errors

I just added my Apple ID to a new MacBook Pro and tried to turn on iTunes Match. This is the error I get:

The only info I can find indicates this is a connection error, but I can connect to other areas of the iTunes Store. Any ideas how I can resolve this?

According to this discussion or this one it seems (-54) is a file-lock problem. The proposed solutions are:

• an AppleScript to remove locks
• use Terminal to ensure ownership, group, and permissions are correct
  • use sudo chown your-username your-filename if you don’t own the file/folder
  • use sudo chgrp staff your-filename if it isn’t set to the same group as other iTunes items
  • use chmod 666 your-filename and/or chmod 777 your-folder-name to make sure everyone (and thing) can edit
• disabling FileVault if used

In particular, check the permissions on the iTunes/Download folder which is where iTunes will first attempt to download “matched” songs.

It’s a permissions denied error.

• Are you sure your Apple ID hasn’t been linked to more then 5 devices?
• Have you tried to log out- and in again?
• Has iTunes Match worked before?