Eddy is right, the file cannot be accessed because it's protected by the operating system. Disabling system restore should help.
In any case, you don't have to worry about the file. Nimda [Drp] is a small piece of code that Nimda worm appends to HTML files. The purpose of this code is to activate the real Nimda worm that should be placed in the same directory. Without the real Nimda worm body (which is probably your case), the code is not dangerous.