When I first started in AS3, there were two blocks that caught me up a
lot. I started from an older AS2 FLA and then converted to AS3 - that
was the cause of the problem.
If you do that, you end up with an AS3 fla that doesn't have the right
settings in the AS3 Properties panel. You won't have automatically
declare stage instance set, or strict mode (you want both).
Also, to get actual line numbers with errors, you'll need to check
"allow debugging" in publish settings - I know it sounds like it's a
permissions thing, but it really enables debugging symbols to be
embedded in the swf, so that when you get an error, you'll actually get
a useful error number with it.
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