Get exclamation point alert icon when opening most pictures in iPhoto My Library appears to be intact.  All the events and albums are normal in thumbnail view but when I open a picture I get this exclamation point error icon that fills the screen. 

Looks fine in thumbnail mode, 
exclamation point alert but I get this error icon when I try to open the picture. 
problem 

Haven't ever seen it before. I recently upgraded to iPhoto '11 (9.3.2) and Mountain Lion and switched out my Macbook hard drive. I imported my iPhoto Library from my old drive using Apple's Migration Assistant. 

I realize that I have a lot of variables.  I have tried many fixes: starting up iPhoto holding down Option and Command, trying all of the repair options, checked the permissions on the photos, rebuilt the Library and none of them have worked. 

What else should I do and or try?
The ! turns up when iPhoto loses the connection between the thumbnail in the iPhoto Window and the file it represents. 

Surefire fix: Restore from backup. Otherwise...

Option 1

Back Up and try rebuild the library: hold down the command and option (or alt) keys while launching iPhoto. Use the resulting dialogue to rebuild. Choose to Repair Database. If that doesn't help, then try again, this time using Rebuild Database.
 

If that fails:
 
Option 2

Download iPhoto Library Manager and use its rebuild function. (In Library Manager it's the FIle -> Rebuild command) 

This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.

Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one.