Have you selected a Record Source for the form?

I don't think you can move from an actual table to a form if that's what you mean. The shift/ctrl stuff is done inside the Add Existing Fields button.

I think you missed the key word of Choose (or in other words Select).
Shift and Control just enable you to select multiple fields to work with.

You still have to then single Click and Drag them to the form.  
You cant move them via keyboard except with in the form.  Once they are on the form you can use the arrow keys to move the selected fields around on the form.

I found the answer after trial and error as I correctly tried to move a group of fields from the Field List to the form. I had to go to the "Database Tools" tab and then click "Contact and Repair Database". I then closed the database and re-opened it. After that both the Shift and CTRL worked correctly to move fields onto the FORM.

Always check the Troubleshooter for weird problems.