Back Up in Acronis True Image Home in 2010

Please can someone help me I am using the above mentioned software in particular the Back-Up when all of a sudden it's started to fail every time the scheduled back-up is to complete. I have it to back-up once a week on a Wednesday and it usually tells me it's going to back-up with an icon in my task bar, however just recently it starts and 5 minutes in pops up and error box saying it failed to back-up if I don't take action now the back-up will stop altogether. I have the back-ups going into an external hard drive and the event code that popped up was 0x00040001+0x0010C45A+0x0000FF0+0x80070008. If anyone can shed any light on why it's failing and how I can fix this please give me instructions in basic form, I'm no computer whizz and have trouble with complex solutions. Thank you.