I keep getting an error trying to search my archive
The email system used to have a separate archive facility, as such there may be a folder called 'Search archive' still visible in your email account. However this folder directly points to the archive software which has now been decommissioned and so clicking on this folder you will either be asked for login details and then get an error message (regardless of what data you enter), or will immediately get an error message.
How do I search for an email that was in my archive?
All the data from the archive was restored to your email account prior to migration of your account in 2011/12. Therefore when looking for any emails that were in the archive, you need to do a search across your mailbox. All emails were restored back to the folder they were in before they were archived (i.e. if the email was in your Inbox folder before it was archived, then it will be back in your Inbox folder now).
If you archived to a local file, then see the FAQ about archive locations and you should be able to open and search this file from the Outlook client.