WSS3.0 Access Denied Error on Multiple File Uploads to Knowledge Base

I noticed a weird quirk today with the error message thrown during Multiple File Uploads.

A user contacted me having problems uploading three PDF files at once via the Multiple-File Upload option, into a Knowledge Base (although I would bet it's the same for a normal Document Library).

It turned out that two of the three filenames had extra periods between the filename and extension - for example:
Filename1...pdf
Filename2...pdf

And apparently Sharepoint didn't like this naming convention.

The weird thing was that the error message being returned to the user was simply:
Access Denied.
And it was the standard Access Denied page with the "sign-in as someone else... or request access.. etc" options.

Nothing at all was mentioned about filename problems.

I finally had them try a single file upload with just one of the files - and that's when we finally saw the real error message display explaining the filename issue.

Such a simple problem - with such a confusing error message displayed.