User ' NT authority\network SERVICE ' login failed.

First step: Add ' NT authority\network SERVICE ' to the Administrator group  
My Computer--right-- > Management-Local Users and Groups  
Select Groups-double-click administrators-->, clicking Add-click Advanced, click Find Now- In the list below, select Network SERVICE user--two times click OK-Join.  

The second step is to add netword service user   in Enterprise Manager;
Open SQL Server Enterprise Manager--Select DB Instance--Open the Security node--Select Login-- > Right-click in the list on the right--select New Login--On the General tab, click the button next to name ...-Select the Administrators group--Click the Members button below--select Network Service-click the Add button-click OK to return to the new Login dialog box-Ensure that the authentication type is Windows authentication and allow access-click OK-Close Enterprise Manager " 

Step three  
rerun the ASP. Database connection string Select Windows Authentication.

Open SQL Server Enterprise Manager--〉 Select a DB instance--Open the Security node--select "Login"--〉 the user area on the right, the "NT authority\network SERVICE"--〉 properties--〉 the servers role, Select "System Administrators" and "OK" in the options below to close Enterprise Manager--〉. You can do it!!!

User ' NT authority\network SERVICE ' login failed.