I got the same error in:
Microsoft SQL Server 2000 - 8.00.760 (Intel X86)
Copyright (c) 1988-2003 Microsoft Corporation
Enterprise Edition on Windows NT 5.2 (Build 3790: Service Pack 1)
The error:
http://i16.tinypic.com/2hwjhpx.jpg
While selecting a backup device (file) during a restore of a database, this error occurred in the Enterprise Manager. Previous to this message, the button "select devices..." didn't respond.
I have no clue... anyone?