Generally when you get an error like the one you have something is mess up in the 
file
system 
table. (/etc/fstab).
Code:
moe@StinkPad:~$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda1 during installation
UUID=f4f171ea-4997-4d79-953d-0d8b578ded24 /               ext4    errors=remount-ro 0       1
# /garage was on /dev/sdb1 during installation
#UUID=9cdec3c2-67b9-4a95-a503-2ee960387bd0 /garage         ext4    defaults        0       2
# /home was on /dev/sda3 during installation
UUID=b2b20155-17be-42cc-b3ce-307696d11587 /home           ext4    defaults        0       2
# swap was on /dev/sda4 during installation
UUID=48e57dcc-834e-474f-9c49-bfb4bfec9bcc none            swap    sw              0       0
moe@StinkPad:~3$ 
If I've altered the system, say in this case I don't have the USB drive that is normally connected and part of the 'normal' system, whenever I boot the system flips out because 
/dev/sdb1 is not there.
If the change is temporary you can hashtag (
#) out the line 
Code:
#UUID=9cdec3c2-67b9-4a95-a503-2ee960387bd0 /garage         ext4    defaults        0       2
 or if it's a permanent change delete the line.
Code:
sudo medit /etc/fstab
I've no idea what's going on in your system, things 
sr tend to be a strain of cdrom drives, however.
To read all the goodies that get logged faster than you can read try:
Code:
dmesg | less
 <space> and 
<b> to move forwards and backwards.