If you have the salary bug, it might make just enough difference to use up your remaining $3 M. I believe the top league salary for a QB is around $17 M = $14 M + $3 M.
The good news is that it didn't let you enter negotiations, so the bug should go away if you wait until the next week to try and re-sign him.
If you still can't re-sign him, do an experiment and cut some players until you can see what he's asking for. If the numbers don't add up, post what you're seeing and I'll see if I can figure it out.