Cita: In HTML, one can specify two different submission methods for a form. The method is specified inside a FORM element, using the METHOD attribute. The difference between METHOD="GET" (the default) and METHOD="POST" is primarily defined in terms of form data encoding.
http://www.cs.tut.fi/~jkorpela/forms/methods.html
Esto significa que si no defines <form
method="POST"> tu formulario se manda por QueryString, y entonces debes recibirlo con
Request.QueryString("chk_turno") o como
Request("chk_turno").
Esto del copy-paste de códigos tienen sus riesgos
