Flash 9 Actionscript Errors

I get an Actionscript error, as soon as the page loads from a URL like
http://SITENAME/ger/ezmultiupload/upload/162/
(162 is a valid node ID)

"TypeError: Error #1034: Typumwandlung fehlgeschlagen: "" kann nicht in Array umgewandelt werden.
at Function/http://adobe.com/AS3/2006/builtin::apply()
at ()
at flash.external::ExternalInterface$/flash.external:ExternalInterface::_callIn()
at ()
"

(Type cast fails... "" cannot be cast to an Array)

WinXP, IE7, Flash Player 9, ez 4.0.1
I'm quite sute, that we can track this down to the Flash Player version, as it used to work until i updated the Flash player.

I also received a longer Error message, but i cannot reproduce this at the moment.

I also have occasional problems with upload 1-2 MB files in FF3. (WinXP, Flash Player 10, ez 4.0.1, no Actionscripts errors displayed).

Any ideas?