Converting Data types

Conversion failed when converting the varchar value 'caID' to data type int............... error is there............ my code is as follows:
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        DataTable dt = new DataTable();
        string query = "select * from Category";
        SqlConnection con = new SqlConnection(@"Data Source=... ...");
        try
        {
            con.Open();
            SqlCommand cmd = new SqlCommand(query, con);
            SqlDataAdapter adp = new SqlDataAdapter(cmd);
            ...