O/S MS Windows 7

C Drive 250 GB
E Drive 1 TB
F Drive 75 GB

Hi Guys

I was wondering if you could help me before I head down to the local Dell service centre I use a 17 inch Alien all has been going well up to now , Since April for some reason it will no longer makes a back up from C drive to E Drive . All I was getting was E drive was full but from looking at  Drive E there was 763 GB Free so it made no sense any way  I delete all the old back ups plus I ran CC cleaning plus I checked E Drive for any problems but nothing found after scanning the whole drive .

I did delete all backups from last years plus I ran CC clean to remove all the old temp files and left on Drive E  763 GB so there is tons of space however it still wont let me back up But there is 763.GB available so it makes no sense ? All I get when I attempt to back up the C drive is error code 0x81000019 .
I suppose some program has changed something in the registry so that it is no longer possible to use the M/S software to backup, whether maliciously or other, one never knows.