Ugh. Let's start with the most basic thing: shut down everything and restart it, one by one, your Mac first and then your peripherals and then attach your peripherals and mount your external drives. Run Disk Utility and Repair every non-system drive (this the "Repair Disk" function in Disk Utility, _not_ the "Repair Database" function Aperture provides.
Does that allow you to "reconnect all"?
Thanks for the ideas. I followed your tips and repairs were made to both the MBP and the external yet the problem still continues with the yellow triangle and "!" I'm also experiencing many other little glitches with Aperture (unable to export certain files, crashing, and general slow speeds when using brushes). All in all I'm very close to going with Lightroom but with the rumors of Aperture 4, I'm temped to hold on a bit longer.
Any other ideas to get rid of these yellow triangles?
When I 'control/alt/clicked' and chose "repair database" in Aperture, it quickly said there was a problem and I had to "Rebuild the database". I first quit, and made a backup just in case, then went back in and chose the "rebuild" option. IT WORKED. All the yellow triangles are gone and it even fixed a couple of the glitches with exporting I was having.
Thanks for your guidence Kirby and hope this helps others.