[X4U] Sleep issues with v10.5.6

[M.Milligan]

Has anyone else experienced this since the v10.5.6 update?

I put my iMac to sleep with the sleep button on the blue apple.  
Sometimes when I awaken the iMac, I need to do a warm boot. It simply  
won't wake up.

Sometimes it works OK, there's a few seconds interval before it wakes  
up once the mouse or key board is touched.

Do I need to do something, set a radio button to on or off somewhere  
in v10.5.6?

I thank you all in advance for your constructive assistance. Cheers,  
and Happy New Year and Sol Invictus to all.

Murray
Medicine Hat, AB