You'll need to write some code to do this. There are 2 main options:
- Use server-side code (plugin or workflow activity) that runs when an activity is created, or the activity state is changed. This code would check if all the activities related to the entity are completed, and if so, deactivate the main entity
- Use client-side code that runs on the Onload event of the form. This would query CRM to check if all activities are completed, and if so, deactivate the fields on the form
Microsoft CRM MVP - http://mscrmuk.blogspot.com/ http://www.excitation.co.uk