This happened to me just a few days ago. Yesterday, I reinstalled ubuntu and it worked for a while. Today, however it's started again. The actions that I took during my last login are two numerous to immediately pinpoint which one may have caused it, but the most likely candidate is that right before I tried to shutdown, I had just modified the fstab with the line:
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto,exec,utf8 0 0
i.e. I had just created a fixed mount point for my cd-rom drive to better take advantage of wine. I don't know if this has anything to do with this problem though.
This happened to me just a few days ago. Yesterday, I reinstalled ubuntu and it worked for a while. Today, however it's started again. The actions that I took during my last login are two numerous to immediately pinpoint which one may have caused it, but the most likely candidate is that right before I tried to shutdown, I had just modified the fstab with the line: exec,utf8 0 0
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto,
i.e. I had just created a fixed mount point for my cd-rom drive to better take advantage of wine. I don't know if this has anything to do with this problem though.