Resource loading woes

I've been using Doom Builder for a long time now, and just today it decides it won't load my pk3 anymore. It returns to me the following error message:

"Unable to load resources from location "C:\Resource.pk3". Please make sure the location is accessible and not in use by another program. The resources will now be loaded with this location excluded. You may reload the resources to try again.
ArgumentException when creating data reader: An item with the same key has already been added.)"

The file is not being used by any other application at all. Restarted twice already, nothing. Anyone have any ideas as to what this could be? Thanks in advance.

Have you tried loading Resource.pk3 from somewhere other than C:\ root?

As a matter of fact that's not the folder it's normally in, I moved it there in an attempt to try and locate the source of the problem. It's been in the desktop, my documents, in about 3 different folders after that...still banging my head against the desk.

Looks more like there is something in the PK3 that DB doesn't like... such as twice a file with the same filename perhaps?

It's the only pk3 with that name in the whole computer. =/
I did notice I'm running a somewhat older version than the one on the DB site...I'm going to try completely uninstalling the one I have and installing the new one as soon as I am done with work. Will update on my findings. Thank you for the replies! :)