What does "stack was produced by a newer version" mean?

[Graham Samuel]

I have a desktop app I've been developing on a Mac running Lion 10.7.5. I have just switched my LiveCode version to 6.1.3.

Part of my app copies a template stack into an area where it can be manipulated and saved (in fact it's in a folder in the 'Applications Support' area of the Mac library). The copy is just a statement:

   put URL ("binfile:" & tTemplatePath) into URL ("binfile:" & gdataStackPath) 

After this is executed, the Mac finder shows the file in place with the expected '.livecode' extension.

Then at some later point in the app's script, I execute:

   go stack gdataStackPath

This has been working for ages. I now have a problem that I may have created myself, but so far I can't find out what I've done wrong: the 'go' command fails to execute, and after investigation I see that 'the result' returns "stack was produced by a newer version", and if I try to open this copied stack directly in LC, by right-click and 'Open with...", I get "unable to open stack: stack is corrupted, check for ~ backup file". Which of these error messages is the right one, and if the first one, what does it mean? I can't see that my innocent 'put URL' can have corrupted the stack, which is not opened until my 'go' command, and therefore not subject to being corrupted.

Can anyone suggest what's wrong? I will continue to look for reasons of course,  but right now I'm stumped.

Graham