Take a good look at the URL in my previous post about the meaning and position of the parameters. Here is some sample code to help you:

declare @exists int

set @exists = 0

if@exists = 0

begin

/*

RAISERROR ( { msg_id | msg_str | @local_variable }

{ ,severity ,state }

[ ,argument [ ,...n ] ] )

[ WITH option [ ,...n ] ]

*/

-- specify ad-hoc message with severity 10:

raiserror ('The system cannot find the file specified.', 10, 1)

-- creating, using and removing a custom defined message:

exec sp_addmessage @msgnum = 50004, @severity = 10, @msgtext = N'The system cannot find file ''%s'' specified.';

raiserror (50004,10,1,'FILE')

exec sp_dropmessage @msgnum = 50004;

end