error occurred during the backup process

I am using Win7 home edition and Comodo Backup 4.4.1. I am backing up to an iomega external USB disc, which works fine. I have started consistently getting the error message “error occurred during the backup process,” and the backup does not run. The backup, which is incremental, worked the first couple of weeks I had it. I haven’t added more files to my computer since then. Any idea what’s up? Also, Comodo, can we get a more specific error code?

Thanks, all.

Paul in Jersey City