while working on of my project with flex for presentation and Java at backend, I come up with this error, which according to Adobe forum http://forums.adobe.com/thread/535105, In my case it was due the missing of RSL(flex Runtime Shared Libaray)osmf_flex.4.0.0.13495.swz or osmf_flex.4.0.0.13495.swf file which is not compiled with FB4. I fixed this problem by placing the mentioned file with my main swf file. alternately this can be done by changing the flex build path i.e from Library Path change the Framework linkage to 'merge into code'. :)
