The stock gallery feature is a forum.
All forums need to be in a category. They don't need to be in a different category that your other forums are in.
So I really don't have a answer on how not to display it as a forum but still be accessible from a hyperlink.
As far as you error goes.
What did you enter in:
Total # of gallery images
and
Maximum size of gallery images
Also for the maximum size setting there is a note that tells you:
Max size set in php.ini is ???
What is that value?
