Unable to set project quata in openstack Juno

Issue

• While trying to set project quota to "-1" I get the following error

"Danger: There was an error submitting the form. Please try again."

• Logged in as admin tenant when error occurs

• It seems that a lot of task involving modification of projects fail with an HTTP 500 error. For instance I can create a new project as admin. But then I cannot modify users, e.g. I can't add users to the project .

ClientException: The server has either erred or is incapable of performing the requested operation. (HTTP 500) (Request-ID: req-6a606692-8365-4b13-a584-138264e10079)

Steps to reproduce:
1. login as admin
2. create new project
3. create a user
4. back to the project and edit it
5. change user from member to admin
6. press save -> error "Danger: There was an error submitting the form. Please try again."