“”Outlook is using an old copy of your Offline
Folder File (.ost). Exit Outlook, delete the .ost file, and restart Outlook.”
If this error pops up, please try deleting the offline file or OST file and restart outlook. OSt file should be
ideally located at C:\Documents and Settings\user name\Application Data\Microsoft\Outlook
If the issue still persists, please follow the below steps to fix it.
1) In Control Panel, open the Mail item.
2) Click Show Profiles.
3) Select your profile, and then click Properties.
4) Click E-mail Accounts.
5) Select View or change existing e-mail accounts, and then click Next.
6) Select the Microsoft Exchange Server account, and then click Change.
7) In the dialog box that contains your mailbox server and user name, click More Settings.
8) In the Microsoft Exchange Server dialog box, click the Security tab.
9) Click to select the Encrypt data between Microsoft Office Outlook and Microsoft Exchange Server
check box, and then click OK.