Invite External Users: Failed to Add the User, Please Try Again

Hello,

I've been getting this error in all three browsers I've tried this morning (Firefox, Chrome and IE):

Reproduction procedure is fairly simple:

1. Go into project management for one of your projects

2. Try to invite and external user in the client role

3. Error

Wondering if anyone else is having a similar issue or if it might be that one of my projects is bugged.

Edit: I'm getting the bug in all of my projects for all user roles, not just client.