You can find the latest troubleshooting information at:
How to get support
For information about the support provided for your edition of Google Apps, open the Support tab in your Google Apps control panel.
For information about the support available to help you through your migration, see the Google Apps Technical Transition Guide. Available support includes deployment resources, Help Center articles and training, technical support, and customized deployment options.
How to cleanly remigrate a user s calendar.
You may need to remigrate a user’s calendar if there are changes to the user’s calendar after initial migration. To completely remigrate a user’s calendar, follow these steps:
Delete the user’s calendar within Calendar Setting on the Google Apps account to remove all existing appointments to that calendar.
Configure the Migration tool to migrate the Calendar and select the option “Migrate all data (overwriting previously migrated data)”.