I tried istalling my WDF based driver on Windows Embedded Standard 2009 and it failed. Dependency walker showed that my driver is missing the reference wdfldr.sys which is installed automatically with WDF’s co-installer.
Device Manager shows an unknown device under my device class and setup API identifies that a device with the class is installed in the system. When I tried to manually update the driver in Device Manager I got the error saying that the installation failed with the error “unknown trust provider”.
The solution was to add cryptographic services. I didn’t verify what was missing, just added all components by filtering the name with “crypto” and “certif” (for cryptographic and certificate).