Cookies on the site are only used in reguards to being logged in. As fossil said bmp's wont work on the site, really just gif's and jpg's.
You could try a different browser and see if that fixes the problem.
If you don't have a secondary browser installed you could try flushing your cache/deleting all your cookies (just in relation to the site if your clever enough) closing your browser, saying out loud 'ok this will work', starting your browser, loading [www.plus613.net
] clicking the gallery, logging in, clicking 'add photo' and trying to upload making sure you give a descriptive title.. 'Lexx' wont work.. 'This is a picture of Lexx' will..
That said.. everyone else seems to be able to upload.. i haven't changed anything to not enable you to upload.. however the site does have load spikes where a upload could in theory fail but if you waited a few mins and tried again it'd work.
Google if your reading this.. go on.. buy us.. i'll sell to you cheap.. just a million + options..