If you're getting error when you deleting a column from a sharepoint list you must run these commands step by step.It works!

using (SPSite mySiteCollection = new SPSite("http://your_sharepoint_site_name")) {
    using (SPWeb web = mySiteCollection.OpenWeb()) {
        try {
            SPList list = web.Lists["Name_of_Your_List"];                       
                       
            SPField f = list.Fields["name_of_your_column"];
            f.ReadOnlyField = false;
            f.Update();
            f.Sealed = false;
            f.Update();
            list.Fields["name_of_your_column"].Delete();


        }
        catch (Exception ex) {
            Console.WriteLine("Error Message is : {0}", ex.Message);
        }          
    }
}

E2