Syncing your Google Apps Calendar with Nokia S60 phones (e.g. N97, 5800XM) used to be easy if you followed the instructions at http://www.google.com/support/mobile/bin/answer.py?hl=en&answer=147951 but as of late October 2009 it suddenly stopped working for some reason, giving just "Your account does not have permission" whenever a sync was requested.

A bit of digging around found that Google Apps has added a 'Mobile Settings' section and turned off mobile synchronisation by default (how helpful; thanks for the warning, Google).

To re-enable syncing of your calendar to your phone, log into your Google Apps Dashboard, select Mobile Settings, and tick 'Enable Google Sync' which should fix it.