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 problem.
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.