When modifying attribute values from the workfile window, you are attempting to modify the values for all the listed objects. We currently do not allow the modification of particular attributes for a set of the objects from the workfile window. Attributes such as 'Description' may be modified but not conversion methods.
You will have to change the value for each individual series. This can be done by opening the series and selecting Properties->Freq Convert.
You will have to change the value for each individual series. This can be done by opening the series and selecting Properties->Freq Convert.