So first check your Mac’s AudioMIDISetup (you’ll find it in Applications>Utilities) that the audio interface you are using is set to 44.1kHz.
If that does not fix the hang, here are two additional solutions:
1) Quit eJamming,
2) move the following files to the Trash:
User> Library > Preferences > com.ejamming....plist (any files)
User > Library > Application Support > eJamming (whole folder)
If eJamming still hangs, you can try this to remedy the Core MIDI problem:
Open your Mac's Terminal.app and enter this command:
sudo rm -rf /Library/Audio/MIDI\ Drivers/*
During upgrading to Snow Leopard's account Migration, the user/library/fonts come over. The order of font migration usage is first "user" then "system". Sometimes there are duplicate fonts and missing fonts. If user fonts are missing, that can cause a hang.
Use the Mac's Font Book application to delete all the user fonts and then eJamming should work. Note: if you have some special third party fonts you should back them up first, clean the user font area, then bring back your special fonts.
So another tip for users who migrate to snow leopard is to check the user fonts, make sure there are no duplicates or missing fonts. For new snow leopard accounts this is not an issue only for those who migrate.
Set up eJamming to start up under Rosetta. Once you start it up once, it is reported to start up both as an Intel and PowerPC (Rosetta) executable.