Can't open archive

[jmt356]

When I try opening my archive folder “Archive folders 3 (2009),” which is located in the All Mail Folders window to the left of the Inbox area of my Outlook window, I get the error message “Unable to expand the folder. The set of folders could not be opened. The server is not available. Contact your administrator if this condition persists.”

I don’t get this error message when I open my archive folder “Archive folder 4 (2010).”

When I try to open ArchiveFolders3.pst, which is the Office Data File on which Archive folders 3 is based, through the Open Outlook Data File dialogue, I get the error “The file …\ArchiveFolders3.pst is in use and could not be accessed. Close any application that is using this file, and then try again.

Why the errors?

[HansV]

Have you tried rebooting your PC?
If that doesn't help, try repairing the pst file. See How to use the Inbox Repair Tools to recover e-mail messages in Outlook 2002, Outlook 2003, and Outlook 2007 for detailed instructions.

[jmt356]

Rebooting worked.