Let's start at the beginning.
If you plug in the ZTEX Boards for the first time and you have not got ANY software from ZTEX on your machine, the system should initially not be able to assign a driver to this USB device. Making it unusable for now.
Or
If you have played around with the BTCMINER software from ZTEX and according to those instructions have made libusb (of ZTEX) available, the ZTEX Module will show up and have that driver associated with it. In this case, and if you have JAVA (sdk or rdk) on your machine, you could run BTCMINER as instructed by ZTEX and verify that the boards are ok.
In EITHER case, getting zadig.exe will allow you to assign a sort of "default" driver to the ZTEX module, either by assigning it or replacing the libusb of ZTEX, depending on the case described above. This default driver is the one that cgminer is happy with. The ZTEX BTCMINER, if you had ever used it, is then no longer happy, it needs the old one.
Use zadig "Options" "List all Devices". In my case, in the list I found ZTEX Module, because I had previously run BTCMINER (Case #2 above).
I then told zadig to change the existing Driver to WinUSB (see the place on the menu with the green arrow and the button to press).
After the confirmation success, I was able to run cgminer but no longer BTCMINER.
Consider zadig.exe to be a sort of quick and dirty way to change USB Drivers on the fly. Without zadig, you need the whole rigmarole of uninstalling, resinstalling etc. of the drivers in the system, which can be very tedious.
To verify that your zadig experiment was succesful, consider executing cgminer thusly before attempting full scale mining, this will save some time:
cgminer --ndevs
you should see:
D:\BTC_Mining\TestcgminerZTEX\cgminer-3.1.1-windows>cgminer --ndevs
[2013-05-29 23:01:27] CL Platform 0 vendor: Advanced Micro Devices, Inc.
[2013-05-29 23:01:27] CL Platform 0 name: AMD Accelerated Parallel Processing
[2013-05-29 23:01:27] CL Platform 0 version: OpenCL 1.2 AMD-APP (938.1)
[2013-05-29 23:01:27] Platform 0 devices: 1
[2013-05-29 23:01:27] 0 ATI RV730
[2013-05-29 23:01:27] GPU 0 ATI Radeon HD 4600 Series hardware monitoring enabled
[2013-05-29 23:01:27] 1 GPU devices max detected
[2013-05-29 23:01:27] USB all: found 24 devices - listing known devices
.USB dev 0: Bus 7 Device 8 ID: 221a:0100
Manufacturer: 'ZTEX'
Product: 'btcminer for ZTEX FPGA Modules'
[2013-05-29 23:01:27] 1 known USB devices
Before doing the zadig thing, I was getting:
D:\BTC_Mining\TestcgminerZTEX\cgminer-3.1.1-windows>cgminer --ndevs
[2013-05-29 23:03:28] CL Platform 0 vendor: Advanced Micro Devices, Inc.
[2013-05-29 23:03:28] CL Platform 0 name: AMD Accelerated Parallel Processing
[2013-05-29 23:03:28] CL Platform 0 version: OpenCL 1.2 AMD-APP (938.1)
[2013-05-29 23:03:28] Platform 0 devices: 1
[2013-05-29 23:03:28] 0 ATI RV730
[2013-05-29 23:03:28] GPU 0 ATI Radeon HD 4600 Series hardware monitoring enabled
[2013-05-29 23:03:28] 1 GPU devices max detected
[2013-05-29 23:03:28] USB all: found 24 devices - listing known devices
.USB dev 0: Bus 7 Device 6 ID: 221a:0100
** dev 0: Failed to open, err -12