I was finally able to get my gallery .zip uploaded and working, I was even able to use {gallery} in an article to display a gallery. The site sat overnight untouched, and now the I am receiving the dreaded {gallery}1{/gallery} code where the gallery should be displayed. I can still upload within K2 and view the gallery in the backend, but no luck in the article.

I reinstalled a fresh copy of SIG Pro, same issue. I also have noticed that I don't have the showthumbnail.php (not sure if that is correct) file in my plugins>content>plugin_jw_sig folder as others have mentioned.

Please provide me with a link to your site in order to understand your issue...