Disk optimisation. Drive C busy, retry later

Hi there,

 

just finished running a full scan.  Norton disk optimisation is showing "Drive C Busy, retry later".  Any ideas why this is?  Just read somwhere that this could be a sign of my hardrive packing in.  Hope not.  There should be plenty of space as I save everything on to a flash drive.

 

Norton screenshot RB.PNG

 

I would put a screenshot up but I'm not to sure as to how to do this after I've used the snipping tool to take a pic of the window.  I have tried though so hopefully it works and you can see what I'm talking about.  Any help would be appreciated.  Thanks in advance all.