The PracticalAFAS library has been removed from the module. Therefore, this module cannot just be upgraded from 3.0 in one click. I'm sorry for the inconvenience (to the one or two other users of this module).
The reason for this is that non-GPL files are are not allowed to be in the drupal.org repository, and my PracticalAFAS library is released under MIT. I am giving this version 3.1 and not 4.0, so that version 3.0 will be less visible, for this reason.
Install instructions can be found in README.txt.