I think this might be an issue with your webserver/rewrite rules or something like that. + is allowed in titles (although should be encoded as %2B ).

If you change the url to replace + sign with %2B (or replace the underscore with %2B if it got converted to an underscore) does it work. If you include an image in a page with [[image:NameWith+Sign.png]] (use a literal + there), does it work?

Lowering priority till we can get this confirmed as a MW problem and not a config problem.

(In reply to comment #2)

Lowering priority till we can get this confirmed as a MW problem and not a
config problem.

Note, can't be that much of a mediawiki problem given that things like [[commons:File:U+2160.gif]] works fine.

WFM per comment 3. Please re-open if the problem still exists, and it doesnt appear to be a config issue.

mfeldman wrote:

I understand (3-1/2 years and several version later) that this is a somewhat obscure issue, and low priority. However:

UX perspective - If a user of Mediawiki enters a file name through one part of the Mediawiki UI, and gets "file does not exist", then enters the same file name through a different part of the Mediawiki UI, and gets "file already present"

...how can this possibly *not* be considered a Mediawiki issue?