2.7 "corrupts" 2.6.1 stack - Help!

[Alan Gayne]

So here I was, playing with my newly downloaded copy of 2.7.

Stupidly, I used it to open the latest version of a very complex project on which I have been working on a long time, and for which I haven't made a recent backup.

The mainstack opens up with only a few visual anomalies, but after closing it, it refuses to open in 2.6.1, telling me that the stack is corrupted and to try the backup.  Nor will it run in the 2.6 Player.

Interestingly (or perversely if you view it that way), the stack WILL reopen in 2.7, but with the same few visual anomalies.

But even a copy "saved as" will not open in 2.6.1, where I really need to continue the project.

Has anybody experienced this, and is there any way to get back to where I can use the stack in 2.6.1?

A positive solution will save me MANY hours of additional work, and would really be appreciated.

I'm on a Mac Powerbook G4, running 10.3.9

Thanks in advance,
Alan Gayne