You may have found a bug in the AIR installer or packager. Given that the signature is an XML file, the "&" character seems the most likely culprit.
The only short-term workaround is to identify which characters cause the problem and avoid using it.
You should avoid the following characters in any case, since these cannot be used in file names on all platforms:
various 0x00 - x1F
after scratching my head for quite some time, I eventually ran across this post. Having tried uninstalling *everything* (I was using Eclipse+Aptana, and Air SDK 1.5.2) and reinstalling... then trying another computer that installed from scratch Eclipse+Aptana (deleted all metadata in my project folder copy).
Simple - the ampersand that I had introduced in a filename. I hadn't thought of that as being a problem.
So this answer is true - there does seem to be an issue with the packager/installer in terms of filenames with 'special' characters.