As a student, when you receive an activation code - aka Group Key - from your Teacher to establish your NEW user account and encounter an "The activation code does not exist" error, then we recommend the following:

1. Attempt to get the code in a form from which you can copy/past, as opposed to manual entry.
2. Ask your Teacher to double check the code to ensure accuracy.  Mistyping the code .

Note: 0(number) is commonly miss-read as O(letter). In most cases, this character is a letter.