Currently Being ModeratedOct 31, 2012 8:31 AM (in response to Godpork)
What is your garageBand version? Have you updated to the latest version?
How long do you wait, before you force quit GB? If GarageBand is running out of memory, it may take some time, before it manages to drop the loop. Then It would be best to close some other apllications or to reboot the system, if that alone does not fix it.
If you cannot add loops at all, then you may have a problem with corrupted permissions or preferences; then HangTime's "oddball problem fix" may help: See the FAQ: