Stavo facendo delle prove per un form di autenticazione con la convalida dell'imput di un modulo.

mi da questo errore:
codice:
Compilation Error 
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 

Compiler Error Message: BC30289: Statement cannot appear within a method body. End of method assumed.

Source Error:

 

[No relevant source lines]
 

Source File: C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\e-learning-centre\ac47bef1\8b3dc353\App_Web_tmp68sqjw46e6.aspx.cdcab7d2.kehmb88g.0.vb    Line: 89
Ecco il codice.

codice:
<script runat="server">
Sub convalida ( sender as object, e as eventargs)
'CONTROLLO VALIDITA'
if page.IsValid then
'controllo
Else
Response.write ("E' necessario compilare i campi Username e Password per effettuare l'autenticazione")
end if
</script>