Uncaught ReferenceError: CRM is not defined when trying to access mail templates
Here are some places to check:


The JavaScript file name you mentioned shows that you're using aggregated JavaScript.  To troubleshoot this, temporarily disable aggregated Javascript.
If that solves your problem by itself, it's probably just a caching issue.  Clear caches and reenable JS aggregation.  More likely though, it will just make debugging easier (e.g. by showing the actual JS file throwing the error).
Use the "Network" tab in your browser's developer tools once JS aggregation is off to look for 404 errors.