SQL Server IF EXISTS THEN 1 ELSE 2

How about using IIF?

SELECT IIF (EXISTS (SELECT 1 FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx'), 1, 2)

Also, if using EXISTS to check the the existence of rows, don't use *, just use 1. I believe it has the least cost.

If you want to do it this way then this is the syntax you're after;

IF EXISTS (SELECT * FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx') 
BEGIN
   SELECT 1 
END
ELSE
BEGIN
    SELECT 2
END

You don't strictly need the BEGIN..END statements but it's probably best to get into that habit from the beginning.