Why can't I manually release a POB?
When you manually release a POB in the Workbench by clicking Release/Defer POB for the line, an error is displayed in the upper-right corner saying this POB cannot be released manually.
Re: Why can't I manually release a POB?
One possible reason for this problem is that manual release is not allowed for the selected POB.
Go check the POB template definition (navigate to Policies > Performance Obligations) and make sure the Allow Manual Release switch is toggled to Yes for the POB template.