If you have this problem (HIPS cannot be enabled after updating to 9.0.402), here is how I fixed it :
In the ESET interface, go to Tools | Logs | Events and note which drivers have not been installed (generally eamonm.sys and/or ehdrv.sys and/or epfwwfpr.sys).
Reboot in safe mode.
In Windows Explorer, go to C:\Program Files\ESET\ESET NOD32 Antivirus\Drivers. Open the subfolder corresponding to the driver that failed to install, right-click the