/tmp is probably mounted as read-only OR your disk is at 99% capacity (although in that case, lots more would stop working too).

In ssh check the mount list:
Code: 
# mount
/dev/sda3 on /tmp type ext3 (ro,usrquota,grpquota)
# mount -o remount,rw /tmp
# mount
/dev/sda3 on /tmp type ext3 (rw,usrquota,grpquota)
Somethin along those lines anyway.