BACKUP never works......Error 0x81000037

I can't find any definitive solution being offered from Microsoft.  I'd say it is a most valuable feature but have never seen it work.  
The error message includes 'failed while trying to read from the shadow copy of one of the volumes being backed up.' How technical do I have to be to conduct such a fundamental tack?

I'm using Windows 7 ULTIMATE 64 bit OS and have a couple of large external Hard Drives (2 TB) one of which is the target for the backup. 

An explanation would be most appreciated.  Thanks

geoff