Well unfortunately that's why they call them beta's.
Try here see if it helps, at worst there is a place all the way at bottom to report bugs. I just skimmed over it and saw something about versions and runtimes may not be compatable in some cases, beta 2 vs1-2 and 1.5 and 2 runtimes in CS4:
I received this same error a few days ago and was unable to resolve it, at least intentionally. I had the error and immediately started searching the web for help and came across this page.
I was able to fix it, though I cannot confirm any one action I performed that fixed this. I updated my Flash debug player and removed AIR and reinstalled it with the latest public release version. I also tried quitting Flash and starting it back up. I essentially gave up and used another computer to finish my project. I shut the machine down and came back the next day and it worked!
So my advice is to remove AIR, install the latest version. Also try restarting machine after you do this.
Hope that helps. I wish it was more definitive but the probably is completely gone.
Thank you for your answer.
Although it seems that my problem is solved since I've upgraded to Flash CS5.
Still, thanks again for letting me know.