Can you provide some screenshots of the task configuration and what User1 sees when trying to access and respond to the task?

In general make sure that User1 has at least read access to the item the workflow is running on, and at least Contribute access to the workflow tasks list (most likely named Workflow Tasks).

Gunesh v:

How are you?

I consider that this is a Governance Process issue.

Why?

Because if in the design of your process, you have decided to use a group named "Manager group" and perhaps your process/workflow is considering those user for permissions (for site/list/libraries/items/etc) for another business rules.

If you generate a workaround so as to allow to user1 to be delegated, it's probable you are violating other business rule or process governance.

I consider that user1 should be part of the Manager group or create another group named ManagerDelegates to be part of the task.

I think that in the future we 'll have enhancements about delegations.

I am good..

Thanks for the reply.

Even i know that because of group task it was not working. However I want to know other options to implement those kind of business rules.

As you said creating managerDelegates group is also a good option.