Unable to Acces disk!

[Diahron Grismore]

When attempting to 'Add/Remove Applications' I am asked to insert a 
given disk into the cdrom drive. Once the disk is inserted it can not be 
accessed. Error: Unable to access disk. I managed to get pass this 
previously, but had to reinstall system now it is happening again. If 
there is a setting or steps that I have to take to remedy this please 
inform, or should I 'Bug-List it?'