Can't add to the planner "this action cannot be performed because this file is not modifiable”".

What you need to do is give read/write access to the file below.

You should find it here:

C:\Program Files\Guru Planner 2010\Guru Planner 2010.USR
or here:
C:\Users\logon-name\Guru Planner 2010\Guru Planner 2010.USR
(substitute the logon-name details to that of the user!)

Right –click on the file and go to properties, then the security tab and then edit to change permissions so the current user has Read & Write permissions.