This error also occurs if you did not upload the various rsl/swc/flash-library that your swf file might expect. You may upload this RSL or missing swc or tweak your compiler options cf. http://help.adobe.com/en_US/flashbuilder/using/WSe4e4b720da9dedb5-1a92eab212e75b9d8b2-7ffe.html#WSe4e4b720da9dedb5-1a92eab212e75b9d8b2-7ff5