This is usually a matter of the correct category not being available on the dropdown list to select on the submission page. Likely, the category you're submitting to is a deeply nested subcategory. You'll need to go to settings->general appearance in your admin panel and find the 'number of levels in sitemap' setting. Set this to a larger number of levels than you have... say, 10. Then go to 'regenerate counters' and regenerate your category selector/sitemap. Now return to the category you were submitting to, and you should find that it's properly available on the list and is being selected so that submissions will go into it whenever the submitter doesn't choose the change the category.


Alternatively, if your pages are becoming slower due to the number of categories you have you may wish to read http://scripts.webmastersite.net/wsngallery/manua...