Access denied for a particular file - nothing helps

Hi,

I'm running a Win2003 R2 server with AD (at home for file sharing); yesterday i decided to do a backup by just copying the D: drive onto a 1 TB external drive. On one file it gave "Access denied" error and so far I can't find a way to get rid of it:

1. I'm running as a user with admin rights, but still i changed ownership of the file to myself - didnt help;
2. I checked if file is locked by a process (which would be weird as this file is not used - it's a part of an old archive) - none.
3. I ran couple of different antiviruses overnight - none
4. Ran chkdsk - didn't find any problems

I need to note that problem exists if i try to do anything with the file, even just renaming it.

I'm totally lost - had similar problem in the office with a file on a network share but it helped changing ownership.

Any help is greatly appreciated!

Thank you in advance,
Andrey
.