If you recently updated your computer, it is possible that the EndpointLock was scanning the kernel for unknown drivers during the update, leading to a false positive. Please try restarting your computer and see if the error message reappears when EndpointLock starts. If no message appears then your computer is secure, and no further action is needed. If the message does reappear please follow the steps below.
You may receive the following error message from EndpointLock after updating your PC to Windows 10 Version 1809 (released October 2nd, 2018):
"[NotifyDriver] Failed to deliver keydown event to the driver -> ERROR 6: The handle is invalid."
If you are receiving this error message, right-click the EndpointLock taskbar notification area icon then select "Check for Updates" to download and install the latest version of EndpointLock which resolves the issue.