我做的是 PDA 项目，PC的IE调用WebService 正常，WiFi下PDA里的IE调用WebService 正常，USB下PDA里的IE调用WebService 正常，问题是USB下PDA 的Application里调用WebService就出现 System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> Object reference not set to an instance of an object. 请问这是个什么问题呀？

代码如下：

            bool bDevice = false;

            try
            {
                bDevice = TankService.CheckDevice(DeviceID, SerialNumber());
            }
            catch (Exception e1)
            {
                WriteSysLog(e1.ToString());
                return;
            }