Error on "Assign to Team or User" window in Service and Training request

On the "Service and Training Request" form, when trying to change the Owner field using the lookup button, a popup window titled "Assign to Team or User" (see below screenshot). After a user is chosen and the "Assign" button is pressed, a JavaScript error pops up with:

"An error has occurred. Please return to the home page and try again."

Similar issue reported here: community.dynamics.com/.../513851