Windows – Legacy Kernel Caller preventing sleep mode

power-managementpowercfgsleepwindows 7

I have a problem with Windows 7 not sleeping.

PowerCfg -requests

says a "Legacy Kernel Caller" driver prevents the sleep mode.
This is not very helpful or informative.
How do I get more details about that object?

EDIT:

I found that 

Powercfg -requestsoverride

is the best way of dealing with such misbehaving drivers and software.

The option -requestsoverride is not very well documented.
MSDN doesn't mention NAME is case sensitive, and to remove a request from overrides list you give the option with blank REQUEST parameter.

Best Answer

Thanks for all the suggestions!

Finally I narrowed down the problem simply by trial and error, disabling devices and rebooting. It was a TV card driver hung and not releasing the power request despite being no longer in use.

EDIT:

Unfortunately, the problem with TV card is intermittently recurring. Googling shows it's also quite common. I found that disallowing the driver from making power requests with

Powercfg -requestsoverride Driver "Legacy Kernel Caller" System

solves it.

"Legacy Kernel Caller" is translated on different Windows language versions. On my Polish system it says "Starszego typu obiekt wywołujący jądro".

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