CyUSB.sys downloaded through our website is an unsigned driver. Using it in 64-bit operating system without disabling driver signature enforcement is a possible reason for this behavior.
Following are the steps to disable driver signature enforcement in 64-bit operating system
1. During boot-up press F8.
2. In the list of options that appear select “Disable driver signature enforcement”.
Find KB article Why is CyUSB.sys not WHQL signed? for details on why a signed driver is not provided. Find Application note Windows Hardware Quality Lab signing procedure for details on driver signing procedure.
Note: In the case of Windows Vista 64-bit operating system the error message is “Windows cannot load the device driver for this hardware. The driver may be corrupted or missing. (Code 39)”
In the case of Windows 7 64-bit operating system it is "Windows cannot verify the digital signature for the drivers required for this device. A recent hardware or software change might have installed a file that is signed incorrectly or damaged, or that might be malicious software from an unknown source. (Code 52)".