Flash actionscript inconsistencies. Please help!

I’m a pretty experienced flash developer but I recently encountered an inexplicable problem.

I’m building a flash website with Flash CS3 on Mac OS X Leopard. Now-- this is my problem.

When I open Flash CS3 and my .fla file, and test my movie-- the first time it works flawlessly. If I click check syntax or auto format, it reports no errors.

Now, if I dare try it a second time, the testing of the movie doesn’t work. There are no errors in Output or Compiler Errors, but the SWF panel is blank. If I click check syntax I get the popup: “This script contains errors. The errors encountered are listed in the Compilers Errors Panel.” But if you go to the Compilers Panel, there are no errors listed there. If I click auto format I get the popup “This script contains syntax errors, so it cannot be Auto Formatted. Fix the errors and try again.”. But I’ve pored over ever character of those 5000 lines of code and I know there is no error.

So, if I close the .fla and open it again, same problem.

BUT, if I quit Flash CS3 completely, and open my .fla again, IT WORKS! But just once. Then the same problem again. Blarg!

What the heck is this?

Please do help. I have no idea what’s wrong…