If your Exchange 2010 mailbox has an online archive mailbox associated with it, the name of the archive mailbox shown by Outlook is not the same as the ArchiveName attribute on the archive mailbox.
For example, the following figure shows ArchiveName value for the archive mailbox in the Exchange Management Shell:
In the following figure, the archive mailbox is shown in the navigation pane in Outlook 2010:
In the following figure, the same archive mailbox is shown in the navigation pane in Outlook 2007:
If you review the Autodiscover information received by Outlook (as seen on the XML tab in the Test Email AutoConfiguration tool), the Display Name value matches the value shown above in the Exchange Management Shell.
<DisplayName>Online Archive - E14 User1</DisplayName>
<LegacyDN>/o=WINGTIPTOYS/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=E14 User1/guid=272d7f6c-824e-48ee-ae2e-c2be8a941a4a</LegacyDN>
The name of the archive mailbox displayed in the Outlook navigation pane is currently using the following hard-coded values:
Archive - email address
Archive - display name
At this time, there is no way to modify the name of the archive mailbox that is displayed in the navigation pane in Outlook.