In the previous version, we included NetMocker as a library (SWC), whereas in the latest release we've included the source code instead. (It's located in libs/adobe/NetMocker.) Note that you'll only need this project if you're running the unit tests for OSMF -- if you're not, you can simply delete the NetMocker, NetMockerTest, and MediaFrameworkFlexTest projects and that should cause the error to go away.
I believe the cause of the error is that Flex Builder doesn't inherently know the build order of the projects, so it's something that each developer needs to specify. You can change this via Window -> Preferences -> General -> Workspace -> Build Order. Uncheck "Use default build order", then move projects up or down to match this order: MediaFramework, NetMocker, NetMockerTest, MediaFrameworkTest, then the sample apps (CompositionPlayer, etc.).
Thank you for your refreshing fast response, although I am still not able to load and/or compile the project correctly.
I am quite sure about the fact, that the error is caused due to my lack of Flex - knowledge. I don`t want to steal your time, it seems to be the best idea to go through Flex basics first (in order to find out, how to load an foreign project correctly). As you can (for sure) imagine, someone who is used to doubleclick a .fla file, has to learn a lot about flex.... The only thing which is confusing, is that i can see all the AS3 classes and a bunch of other files and in addition I don`t think there is an NetMocker.swc file at all. Following your advice, i`ve concentrated on a sample app (CompositionPlayer) but now Flex requests MediaPlayer.swc.....
Nevertheless thanks again for your help, I`ll be back when I know the necessary minimum about Flex