We have created a patched version of the OMNeT++ 4.0 (called 4.0.p1), which works correctly with gcc 4.4.x. On some linux distros the IDE also stopped responding on first load because of incompatibilities with some versions of xulrunner (required by firefox). This version now should work without any problem on recent distributions. The windows version is not affected and the latest version is still 4.0.