Javascript error: can docInfo.js become damaged?

I've been trying to add the same two rollover GIFs to a new HTML file that I've
used on many other files without any
problems, however now I keep getting this message:

While executing onLoad in Swap Image.htm, the following Javascript error(s)
occured:
At line 44 of file "...Applications/Dreamweaver
MX:Configuration:Shared:MM:Scripts:CMN:docInfo.js" :
getDocumentDOM: Argument number 1 is invalid

I'm on Mac OS 10.3.4 and using DW MX (although I also have DW MX 2004 and it
does the same thing).
I've tried deleting the Javascript from the file's code and the images and
starting over, and I've copy/pasted
both the images and javascript from files that work. I've even copied the
docInfo.js file from the XM 2004 folder
and placed it into the MX folder, but with no luck. That's all the info I can
give. Any help would be very, very
appreciated as this project is getting very far behind!

Thanks!