Google Forms with file upload questions are not compatible with Shared Drives (they can only be in My Drive). Move/create Google Forms with file upload questions to My Drive to resolve this.

You'll see unexpected behavior from the form if you try to do this:

If you move a Google Form with a File upload question type to a Shared Drive

• When users try to fill out the form, they will get a message that the form is no longer accepting responses.
  
• Form editors will see an error message: "Forms containing File Upload questions are not currently supported in shared drives. Please remove this form from the shared drive."
  

If you try to add a file upload question to a Google Form already in a Shared Drive

• The file upload question type will be grayed out