What I did (Lets see if it works).
1) Go into the screen like you are initiating a new merge. This is actually the same screen to match, reject, compare, or remove. Put in both of the profiles in to the boxes.
2) Click on "remove," which removes any connection between the two profiles.
3) Reinitialize the merge.
Now, the merge shows as pending, so you should be able to approve it.
This is a known glitch that has been seen before. Hopefully it will be fixed soon :)