Process Model

The icon ion the User Input Task node AND the error message are both telling you that you need to assign this node to someone so that they can work the step. Think on a User Input Task as a "service request!" but instead of a "silicon-based REST service" it's calling a "carbon-based service". But in both cases you need a defined end-point. In this case that end-point is configured by setting the Assignment. This can be to a defined user-account or a Group.

Thanks.

It is working now.

After assignment of the user, error disappeared.

But when I start the process (Ctrl+D) I am getting an user input form and after submitting the form nothing is happening.

When you say "after submitting hte form" are you referring to the Start Form, or to the form used on the User Input Task?

If you're talking about the Start Form, we can tell from your screenshot that the process instance has been started and that the User Input Task node has been started and presumably assigned to whatever user/group you chose as the Assignee.  At this point, that task should show up in the "Tasks" list for any affected user(s).  In your process instance, you can view / accept the task by right-clicking on the green-highlighted node and clicking "View Form".

Additionally: If you want the form to be shown immediately to the person who submitted the Start Form (which I suspect might be the case here), you will need to enable Activity Chaining on the process flow line between the Start Node and the Task node.

When you say "after submitting hte form" are you referring to the Start Form, or to the form used on the User Input Task?

If you're talking about the Start Form, we can tell from your screenshot that the process instance has been started and that the User Input Task node has been started and presumably assigned to whatever user/group you chose as the Assignee.  At this point, that task should show up in the "Tasks" list for any affected user(s).  In your process instance, you can view / accept the task by right-clicking on the green-highlighted node and clicking "View Form".

Additionally: If you want the form to be shown immediately to the person who submitted the Start Form (which I suspect might be the case here), you will need to enable Activity Chaining on the process flow line between the Start Node and the Task node.

Also keep in mind that if you use a start form and a user input task they will show as two separate forms and two separate events. How many forms do you expect to show in this process? If it's only one, then you don't need both the start form and the user input task.

If I remove the "Process Start Form" from the process model and when I click on the "Action" link which I have created is not working. Not sure why.

Also, when I click on the Task email I have received through Ctrl+D operation, I goet below error message email.