Administrators do not have unlimited abilities, particularly when the file is in use or considered a system file. However, you can use MoveOnBoot (freeware) to forcibly have the file removed the next time you restart your computer, before the file becomes locked.
Hope this helps,
I have a file on my desktop (a game file that I transfered off a flash drive) that I cannot delete. I am signed into the only account (named 'Ryan') that I have set up on this OS. The file shows full permissions given to Ryan. When I drag to the recycle bin I get a window stating that I need permission from Ryan to delete the file. This doesn't make sense. When asked if I want to proceed - it says it can't.