While taking backups for SQL Server databases onto a mapped drive you might get the following error:
"The system cannot find the path specified."
This is because a network share that you map using a local drive letter will not be visible to a SQL Server instance as it is running as a service. So, the SQL Server service runs in the context of the local console with the security context of the startup account of SQL Server. Also, mapped drives are specific to a session and not visible to a service started in the local console context.
So, if you want to backup a SQL Server database to a mapped drive using a local drive letter you have the following options:
1. Run the following command from a query window EXEC xp_cmdshell 'net use <drivename> <share name>'
-- where
<drive name>: Letter used to map the drive
<share name>: UNC path to the share
2. After that you should be able to backup using the mapped drive letter
3. Your Management Studio Object Explorer logical drive enumeration window should be able to list the above mapped drive


Reference:http://blogs.msdn.com/b/sql_protocols/archive/2007/05/13/sql-network-interfaces-error-26-error-locating-server-instance-specified.aspx