[Applies to: Microsoft Dynamics CRM 4.0]
During synchronization, if you encounter errors that prevent some of your Microsoft Dynamics CRM Online data from being synchronized when you go online, the Synchronizing Microsoft Dynamics CRM Data dialog box opens, and the Error tab displays the list of errors.
Choose this option when you are unable to fix or change errors, for example, if you no longer have access to a record or the record has been deleted. You can also choose this option if you've made minor changes that can be discarded or updated later.
Important Discarding changes made while offline does not revert those changes. You will need to revert those changes manually.
Choose this option if you want to attempt to fix the errors by using the information provided in the Synchronizing Microsoft Dynamics CRM Data dialog box. Any data entered or changed after you went offline will be lost. If you know which records you have added or changed, you can print them out so you can reenter the data later.
More information: Check for Duplicates