security exception

får detta:

Description: The application attempted to perform an operation not allowed by the security policy.  To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file. 

Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.

försöker ärva en klass som finns i en dll som ligger i Bin-mappen

public partial class _Default : Procent.Web.Access.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
...