Could you let us know from which course(along with version) you are trying this use and the respective unit number so that we can have a look into it to understand your use case.
Meanwhile if your intention is to apply the data transform from the Onboarding class then try to provide TGB-HRApps-Work-Onboarding.DATATRANSFORMNAME instead of using pyWorkPage which might work. If not let me know what you are trying to achieve.
Looks like you are trying to perform "Configuring a Work Party" unit from Lesson 9 in CSA 7.2 course. Here in the data transform you need to source the properties from TGB-HRApps-Work-Onboarding page in the EmployeeParty data transform. I had tried a similar use case in my local environment and its working as expected without any errors.
May be you can check any space available in the class name that you might have copied from the clipboard in Pages & Classes as specified in this discussion.
I think in your earlier steps you might have created this class as case creation process or it might be available by default with the provided application. You can check in the application explorer for this class availability.