Troubleshooting: Validation error occurred after adding user

Issue

After adding a user to a role that already contains many users, I receive the following error message:

One or more validation errors exist. Changes will not be saved. Do you wish to continue?

Details

One role cannot contain more than 1500 users. The error message above appears when attempting to add a user to a role that already has 1500 users.

Solution

Create sub-roles under the role that contains 1500 users. Then move the users into the sub-roles. The sub-roles could, for example, be alphabetical groupings of user names.