Created attachment 803385 [details]
Steps to reproduce

Description of problem:
The modal dialog for creating New Task directly in task list freezes (it's 'Create' button is disabled and never reenabled) when you don't fill in any user/group.

Version-Release number of selected component (if applicable):
BPMS 6.0.0 ER3

How reproducible:
Always

Steps to Reproduce:
1. Navigate to Task > Task List
2. Click New Task button
3. Now either
   a) click the 'minus' button next to the prefilled User field
   b) erase the User input field
4. Click 'Create' button

Actual results:
The create button is disabled and the form doesn't display any message to indicate what happened.

Expected results:
Some input validation should be present similar to validation for Task name - e.g. message like 'You must add at leas one user/group' should be displayed near the buttons for adding user/group.

Additional info:
Video of steps to reproduce attached. Notice how the 'Create' button is disabled after clicked.