@chandan31 This is due to the "Assignable by" attribute on the roles that are inherited by the group. Typically, the sn_hr_core.manager role is the Assignable by value for the HR Basic role (as seen below), but you may have additional roles as part of this (contains roles) that require a different role for the individual putting the user in a group. Take a look at these and I am confident this will help address your issue. 

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Regards,

Mike