Comodo Backup stops working

Until a couple of months ago Comodo Backup was working perfectly. Now it reaches the calculation of the backup size and then just closes down. The last entry in the log is “Comodo Backup started”. I have reinstalled Backup but this didn’t make any difference. My operating system is Vista Home Premium.

Has anyone else experienced this problem and how did they solve it?

Subsequently to posting the original problem I have tried running Backup as the administrator and the backup now proceeds to the stage of copying the (first listed) folder and then stops. I have noticed that the

Can anyone please tell me why CBU is stopping as soon as it tries to copy the first folder in the backup?