GarageBand won't work after installing Pro Tools 8 - MIDI Issue?

I recently bought a new MacBook Pro which came pre-installed with Lion. After installing Pro Tools LE 8.0.3 I tried to launch GarageBand but I kept getting a message staing the 'CoreMidi' had quit unexpectantly. When I unstalled Pro Tools, GarageBand 11 opened without issue.

I want to be able to use both GarageBand and Pro Tools on my new computer so I reinstalled Pro Tools and updated it to version 8.0.5. I also updated to the newest version of Lion. Pro Tools seems to work fine, although sometimes it lags when loading MIDI on the startup screen.

When I now try to lanch GarageBand it just bounces in the dock for at least three minutes. When it eventually opens and I try and open a session I started boefore I stalled Pro Tools I get another error message. This one says something there's a MIDI problem and that I should restart the computer or update my MIDI device drivers.

After I click ok, GarageBand is just frozen and I have to force quit it. Restarting the computer does not solve the problem, and Pro Tools as far as I can tell is up to date. I am not actually even using any MIDI devices.

I called Applecare the representitive told me to try re-installing the Lion OS. I started to download it but stopped as I don't want to have to set up everything again and the computer shouldn't need a fresh OS installion after only a couple of weeks. If I knew it would for sure solve the issue though I'd probably do it.

Can anyone help me get Pro Tools 8 LE and GarageBand both working? I am guessing when Pro Tools installs it changes something in the MIDI settings or plugins that GB relies on but I don't want to do anything that might cause more problems. Any help with this problem would be much appreciated.