SqlTableProfileProvider error

I have SqlTableProfileProvider.cs in my App_Code folder but get the following error message when I try to initialize ProfileCommon:
Could not load type 'SqlTableProfileProvider'.
  Source=System.Web
...
StackTrace:
       at System.Web.Profile.ProfileBase.InitializeStatic()
       at System.Web.Profile.ProfileBase.Create(String username, Boolean isAuthenticated)
       at Account_Register.cuwReg_CreatedUser(Object sender, EventArgs e) in c:\Data\projects\asp_Class\Account\Register.aspx.cs:line 99
       at System.Web.UI.WebControls.CreateUserWizard.OnCreatedUser(EventArgs e)
       at System.Web.UI.WebControls.CreateUserWizard.AttemptCreateUser()
       at System.Web.UI.WebControls.CreateUserWizard.OnNextButtonClick(WizardNavigationEventArgs e)< ...