The backup file is unusable.You must erase it, or choose another file

Hello
On my computer, I was doing some important work of mine.
All of a sudden it power cut and when I restarted it, I wanted to open backing archive file which is stored in this Programs/Accessories/System Tool and then an error showed on the screen
"The backup file is unusable. You must erase it, or choose another file".
Now I cannot access my main data stored in the backup files as a result severely my work is getting hampered.
I need to recover these files. What need to do?
Give a solution.
Thanks in advance.
