[VB.NET]Viewstate invalido?!?

[Aki]

sto scrivendo questo codice:

' RECUPERO DATO ULTIMO RECORD TABELLA ### STUDI ###
                Dim SQL5 = "SELECT ISNULL(MAX(ID_STUD), 1) FROM STUDI"
               Dim cmd5 as New SqlCommand(sql5, conn)
                Dim dr5 as  SqlDataReader = cmd5.ExecuteReader()
					While dr5.read()
						Dim stu as integer = dr5.Item(0)
						Dim id_stu as integer = stu + 1
						Session("studi") = id_stu
					end while
               dr5.close()
    ' INSERIMENTO DATI NELLA TABELLA ### STUDI ###
                Dim sql6 as string = "INSERT INTO STUDI (ID_STUD, LIC, VOTAZIONE, QUAL)"
                sql6 &= " VALUES (@id, @lic, @vot, @qua)"
                Dim cmd6 as new sqlcommand(sql6, conn)
                cmd6.Parameters.add("@id", sqldbtype.int).value = Session("studi")		
                cmd6.Parameters.add("@lic", SqlDbType.varchar).value = rl.selecteditem.value 
				cmd6.Parameters.add("@vot", SqlDbType.varchar).value = vote.text 
				cmd6.Parameters.add("@qua", SqlDbType.varchar).value = cbProfe.Checked

ma mi dà sto errore:

Server Error in '/' Application.
--------------------------------------------------------------------------------

The viewstate is invalid for this page and might be corrupted.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: The viewstate is invalid for this page and might be corrupted.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[HttpException (0x80004005): The viewstate is invalid for this page and might be corrupted.]
System.Web.UI.Page.LoadPageStateFromPersistenceMed ium() +140
System.Web.UI.Page.LoadPageViewState() +17
System.Web.UI.Page.ProcessRequestMain() +423




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Version Information: Microsoft .NET Framework Version:1.1.4322.573; ASP.NET Version:1.1.4322.573

che vuol dire?
AIUTO!!!!!! VVoVe:

[Aki]

risolto
era xchè richiamavo tutto col server di webmatrix
con IIS va tutto