I must say that for an "official" Adobe forum on their new premiere product, there is a distinct lack of company involvement here.
The error is because either:
1. The compiler did not recognize or understand a particular metadata tag. If you're using custom metadata tags, let the compiler know: http://krasimirtsonev.com/blog/article/as3-using-creating-custom-meta-metadata-in-flex
2. You have a syntax error which tricks the compiler into thinking there is a metadata tag when there is none. For example: ["foo" + number].
Searching for all metadata tags should help you narrow this down.
I finally spent about 3+ hours going through the code line by line. Comment out a line. Run. Fix? No? Uncomment line.
The problem? A line where I concantanated a string + the value from a database + string. All strings, no numbers, no nulls. Just putting 3 text strings together.
Have no idea WHY this would not work, it just didn't. I've seen plenty of examples of code where a returned database value is concantanated with another string.
The frustration is that if the compiler finds the error, recognizes the error, stops the process....it would seem that it could at least provide more then "invalid metadata error" in an unknown location. I think it knows exactly where the error is.
And the terminology is a bit confusing also. When I think of "metadata", I don't think of text strings being displayed on the screen....