How do you allow a user to set notfication preferences in Cloud Classic

Summary:

We are on OTM 24A, Gen2 and on cloud classic.

Content (please ensure you mask any confidential information):

My colleague gets this when he attempts to configure his notification preferences.

My account does not run into the same error.

I cannot see any differences in the user setting on the UI.

Version (include the version you are using, if applicable):

24A,

Code Snippet (add any code snippets that support your topic, if applicable):