I try to import messages to OE and it doesn't seem to matter which computer
I am on or which identity - even a newly made identity - I try to importr
to, or even which message files I try to import, or where I try to import
them from (though I always try to import .dbx files) I get an error message
reading:

"No messages can be found in this folder or another application is running
that has the required files open.
Please select another folder or try closing applications that may have the
files open."

The only application that sounds like it might be referring to is OE, but
I can't imagine a way of importing without having OE open.

What can I do?
Cheers.