Sudden error using web developer 2008 express

Hi all

I have a login page that calls a simple stored proc to process the user and password against a table. It was working perfectly fine last night and now suddenly i receive this message in regards to the password field:

Quote:

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[InvalidCastException: Failed to convert parameter value from a WindowsPrincipal to a String.]

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the parameter is declared as:

Code:

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Sql.Parameters.Add("@_iPassword", SqlDbType.VarChar, 40)
        Sql.Parameters("@_iPassword").Value = txtPassword.Text

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What would suddenly cause a perfectly working call to this procedure to fail?

Thanks

Are you absolutely sure that that is where the exception is thrown? I doubt that it actually is.