The Planner add-in loads in Outlook - but when a user either clicks on "Book" button in an appointment or choose "My Settings" in the menu - a window opens and shows an error like "An error has occurred - contact your administrator...."
The error can be seen by some users and not necessarily by all users.
A cookie for Planner has gone corrupt - and needs to be deleted.
HOW TO SOLVE
- Open Internet Explorer
- Tools->Internet Options
- Click "Settings" in the "Browser History" section
- Click "View files"
- Find a file like "cookie:login@servername/" (ex. cookie:kasperh@ourserver/"
- Delete this file and restart Outlook and any web browsers that might be open