Disabled files in 2.7

[simplsol at aol.com]

I started using Rev. 2.7 Studio yesterday.
  I quit the program and came back to it later. If I now try opening a 
stack with the Open Stack... menu from 2.7 all of the stacks previously 
opened with 2.7 are disabled (grayed out, do not open).
  If I try opening one of the stacks previously opened with 2.7 from the 
Finder they will open the standalone (which is correct behavior) but 
the stacks, themselves do not open. Trying to open stacks from the Open 
Stack... menu in the standalone is the same as from Rev 2.7: all of the 
ones previously opened in 2.7 are disabled.
  I had been able to work around this by using the Open Recent File menu 
in Rev. Until this evening.
  I opened a stack and decided to make some adjustments to it. When I 
clicked on the Table tab in the Inspector, Rev froze.
  When I restarted I was able to get the Table tab to open. But, when I 
clicked on the Horizontal Grid, Rev froze again.
  Now when I try to open the stack on which I was working (from the Open 
Recent File menu - the only option previously working) I get this error 
message:

 Stack no longer exists in this location

 According to the Finder, the stack still exists, in the same location.
  Any advice would be appreciated. (OS X 10.4.4, Rev 2.7, Al PB 1.67, 1 
gig RAM)
  Paul Looney