Are your Skuid versions the same?  Are both environments running Lightning Experience?

If your non working version is a new page (recently copied?), maybe try to click Generate Page Resources?

Are you declaring your MyClassName before using it? 

var MyClassName = MyClassName.DoSomething(String AccountId);

Locker Services requires you to declare everything.

Ah! I am in classic for both environments but one has lightning enabled and the other does not.   

Welp, declaring didn’t help.  I wonder if this is a skuid version issue.  We are on different versions of Milau 11.2.8 (not working) and 11.1.13 (working). That’s probably the cause.  Not seeing anything in the release notes yet. 

Could still be a locker service issue, where calling apex from within JS doesn’t work anymore.  We moved ours to action sequences, and then call the action sequence from JS instead of directly calling the apex class.

Here’s a post from my colleague when we made the switch, and some links to resources are in the post.

https://community.skuid.com/t/clarification-needed-on-skuid-10-0-0-release-notes-related-…

If you are using any script file and getting “Uncaught ReferenceError:” which means ‘x’ is either a variable or a method which you are trying to use before declaring it using var keyword. This means that there is a non-existent variable referenced somewhere. This variable needs to be declared, or you need to make sure it is available in your current script or scope otherwise , it will endup throwing this ‘x’ is not defined error . This usually indicates that your library is not loaded and JavaScript does not recognize the ‘x’.

To solve this error: Load your library at the beginning of all your scripts.

There can be multiple other reasons for this issue:

** Path to CDN library you included is not correct

** The library file is corrupted

** Working offline

** Conflict with Other Libraries