[CentOS] cannot access file: Input/output error

I have a file on a backup usb drive that I get the following error:

# ls -ls P*
ls: cannot access Power usage.xls: Input/output error

How can I delete this file so that the nightly backup will write out the 
current version to the backup drive?

I tried:

# rm -f Power\ usage.xls
rm: cannot remove `Power usage.xls': Input/output error

Which you can see did not work.

thanks