I sometimes encounter duplicate album entries on Google Music All Access, which looks something like this:

Duplicate entries

When you upload an album to your library, Google doesn’t always match it correctly with their own version. I thought it was because of different song durations, but it’s much simpler than that. Just remove the album artist info and everything works fine. Here’s a quick how-to guide.

Click on a song, open the context menu and select Edit info. If it’s not available, select the other song version instead.

Edit info

Now simply remove the Album Artist field and save your changes.

Song info dialog

You can select multiple entries by holding the Shift or Ctrl key.
If this doesn’t help, make sure that all metadata matches exactly (same album and artist name etc.)