When using an offline folder file (.ost), the Microsoft Exchange Client can stop responding during startup if offline synchronization doesn't complete successfully. You can disable offline synchronization by editing the user's messaging profile as described in the following steps:
1. From the Tools Menu, choose Services.
2. Under The following information services are set up in this profile, select Microsoft Exchange Server.
3. Choose Properties.
4. Select the Advanced tab, and then choose Offline Folder File Settings.
5. Choose Disable Offline Use.
Note
If the problem persists, you may also need to rename the .ost file.