iSync users who keep their contacts and calendars synchronized between their computers and mobile phones may run into a problem where iCal no longer syncs properly, and instead gives an error indicating the lack of an available and ready calendar.
As described by Apple Discussions poster 2ns:
"Recently I noticed the calendar entries on iCal no longer syncs with that of my mobile phone. When I clicked on the icon of my mobile phone in iSync, the check box for the "calendars" is not checked, but whenever I click on the check box the following message appears: "No writable calendar was found: Before you can synchronize your calendars, you need to open a calendar application that supports synchronization and create at least one writable calendar."
This problem does not seem to be related to the phone, since it has occurred for users of various makes and models of phone, including the Nokia N93i and Sony Erricson K800i. As such, users have focused troubleshooting efforts on the iSync application and found that resetting the sync folder seems to be the solution.
Fix: Reset the sync folder Open the iSync application and go to it's preferences. Then click the "Reset Sync History" button at the bottom in the "Advanced" section and confirm the reset action in the popup window. Then select the mobile device again in the iSync application, enable the features that were not syncing properly, and try another sync. If the problem still persists, do a manual reset of the sync folder by opening the Terminal application and entering the following command.
- /System/Library/Frameworks/SyncServices.framework/Versions/A/Resources/resetsync.pl full
When the command completes, follow the same steps above to re-enable syncing on the device and attempt again. Users may be tempted to manually remove their SyncServices folder (located in /username/Library/Application Support/) to fully reset their synchronization, and while this may work it should be used as a last resort. Apple claims doing this can result in duplicate entries for sync information, or loss of sync information. If users attempt this, it is highly recommended they back up their contacts and calendars first. This can be done in iCal and Address Book by selecting the desired information and then exporting (in the File menu) the contents to a safe location.