Issue

Archiving old emails within a mailbox to a .pst file in MS Outlook 2010 fails with the following errors:

Error while archiving folder “folder_name” in store “mailbox_name”. A folder by this name already exists.

Resolution

Normally, having a folder with the same name in archive is not an issue. The error above can occur if there is a folder withing archive has the same name, but there is a mismatch between upper case and lower case letters. For example, a folder within mailbox is named “Invoices“, but a folder in the same location within the archive is named “INVOICES“

To resolve the issue, rename one of the folders to match the case of the other.

Microsoft Outlook 2010
Windows 10 Pro