Quando tenta atachar um .mdf ao Server 
dá erro 5 (access denied).
“Unable to open the physical file ‘c:\Program Files\Microsoft SQL Server\MSSQL1.1\MSSQL\Data\TravCom.mdf’. Operating system error 5 (Access Denied).”
Solução
Now to resolve this you need not to uninstall Sql Express. Just go to SQL express configuration manager and click on Services from the left pane. From the right pane select Sql server service and go to its properties. The builtin login should be “Nerwork Service”, change it to “Local system” and restart the service. thats it.
