SQL Server Login Error

ERROR

"Login failed for user 'sa'. Reason: Not associated with a trusted SQL Server Server Connection."

If tyou get the above error then try

osql /U sa /P passwd /S servname

If the execution give the same error then we can conclude that theAuthentication is not changed to SQL Server and Windows mode.
Open the enterprise manager --> navigate to your server --> right click on the left pane --> choose properties --> select the security taband change the "Windows only" to "SQL Server and Windows".

STOP and START MSSQL Server service

Note:By default the 'sa' password is blank. Change it quickly. Go to the securityfolder (Enterprise manager) of your server and change the sa password.Include this password in your connection string.