Agent Error while performing Assign Rate

When agent is performing Assign Rate, then it is giving the below error:

Failed to assign service provider while assigning rate for shipment/Error_Recalculate_Shipment_Cost

Shipment is planned already and has valid rate record, rate offering, but when performing the Assign Rate through the agent, it is giving the above error, can someone help us with why OTM agent is behaving this way?

Thanks in advance.