Comment Error Some of the Time

I use the same template on many different domains. It was custom made for me. The problem I’m having is with comments not displaying.

The template works for these domains/blogs:

https://www.wrestlingblog.com
https://tna.wrestlingblog.com
https://www.weblug.com

The template breaks for this blog:

https://www.weblug.com/racing/

I get this error:

Fatal error: Call to undefined function: is_wpuser_comment() in /home/spunkz/public_html/racing/wp-content/themes/WrestlingBlog Blue/comments.php on line 28

I’ve taken fresh copies of the template from the first domain and only tweaked it in two spots: The header image, and the location of the css file.

Any ideas would be very helpful!