在学习FPGA的过程中遇到了题目提到的问题，上网查了下，不少网友也遇到了此问题，记录下解决方法。
在win7 32位电脑上面安装ISE 14.7 然后连接黑金AX516开发板，打开一个例子程序下载的时间提示上述错误。
打开设备管理器设备驱动显示正常（其实并没有正确安装）。
问题解决步骤
（1）USB CABLE下载器连接电脑。
（2）打开电脑设备管理器，找到设备对应的驱动，点击右键->卸载->打钩删除此设备的驱动程序软件->点击确定。
（3）我们需要手动安装驱动, 如果操作系统是64位的用户点击我们提供\07_DRIVER\Xilinx USB Cable\nt64目录下的install_cable.exe；如果操作系统是64位的用户点击我们提供\07_DRIVER\Xilinx USB Cable\nt目录下的install_cable.exe。（黑金AX516开发板配套资料/07_驱动/Xilinx_USB_Cable.rar里面有个Word文档有详细说明）。
（4）再次打开软件，ISE软件可以正常连接下载器了。
一个外文的解决方法：
http://ee.ump.edu.my/hazlina/teaching_ESD/teaching_ESD_lab1_adder%20Fixing%20WARNING.pdf
Fixing WARNING:iMPACT:923 - Cannot find cable, check cable setup
Note: I am assuming you are using ISE 14.7 and have installed it to the default location
1. Make sure that the USB pod is connected.
2. Completely uninstall the current driver (e.g., that from the prior ISE tool release).
This should be done through the Device Manager
(right-click on Start Menu -> Device Manager -> right-click on Xilinx USB Cable -> Uninstall
-> Tick the checkbox Delete the driver software for this device -> OK).
NOTE: It is important to ensure that Microsoft Windows performs a complete uninstall.
3. After completely un-installing the driver, disconnect the USB pod from the computer.
4. Run the "install_drivers.exe" program from C:\Xilinx\14.7\ISE_DS\ISE\bin\nt64\.
Right-click on the "install_drivers.exe" program and select Run As Administrator.
The "install_drivers.exe" program launches an MS-DOS command prompt window that closes
automatically when finished.
When it is finished, re-connect the USB pod to the computer and try again.