What role is required to 'nominate' a user using BPM API's?

I see an exception while nominating a user using SAP API's. Log as below:

Caused by: com.sap.bpem.tm.exception.InvalidAuthorizationException: User Test1 is not allowed to perform action NOMINATE on task 3v67h898881811e4bae5000000ddc0f1

Nominate works fine if the user is assigned "Administrator" role. Is there an alternative role which can be assigned as we cannot give end user admin access.

Thanks in advance

Regards

Vidya