Operation must use an updateable query

Når jeg kører dette script:

strSQL = "SELECT * FROM optaget WHERE Dato = '" & Request.Form("dato") & "' AND Tidspunkt = '" & Request.Form("tid") & "' AND Behandler = '" & Request.Form("behandler") & "';"
Set rs = conn.Execute(strSQL)
if rs.EOF OR rs.BOF then
strSQL = "INSERT INTO optaget (Bestilt, Behandling, Behandler, Dag, Dato, Tidspunkt, Navn, Adresse, Postnr, Bynavn, Telefon, Email) Values ('" & Request.Form("bestildato") & "','" & Request.Form("behandling") & "','" & Request.Form("behandler") & "','" & Request.Form("dag") & "','" & Request.Form("dato") & "','" & Request.Form("tid") & "','" & Request.Form("navn") & "','" & Request.Form("adresse") & "','" & Request.Form("postnr") & "','" & Request.Form("bynavn") & "','" & Request.Form("tlf") & "','" & Request.Form("email") & "')"

Conn.Execute(strsql)
else
  Response.Redirect "xxx.asp"
end if

Conn.Close
Set Conn = Nothing

Får jeg denne fejl :

"Operation must use an updateable query"

i linie 15, Conn.Execute(strSQL)

HVORFOR ????