I also experienced this bug after upgrading to 12.04 from 10.04.
After chaning settings using Ubuntu Tweak, I could not login using LightDM at all. Switched back to GDM and was able to login & debug the issue.
Yes, I had DISALBED the login sound using Ubuntu Tweak. After re-enabling the login sound, I switched back to LightDM and was able to login perfectly. This appears to have something to do with the login sound and/or timing upon login.
AGAIN, re-enabling the login sound appears to correct this issue.
I also experienced this bug after upgrading to 12.04 from 10.04.
After chaning settings using Ubuntu Tweak, I could not login using LightDM at all. Switched back to GDM and was able to login & debug the issue.
Yes, I had DISALBED the login sound using Ubuntu Tweak. After re-enabling the login sound, I switched back to LightDM and was able to login perfectly. This appears to have something to do with the login sound and/or timing upon login.
AGAIN, re-enabling the login sound appears to correct this issue.