Lockup on Suspend

My MacBook Pro has started crashing when I wake from suspend. This has happened to me several times recently, and I'm not sure how to go about diagnosing it.

When I leave the office I disconnect the external monitor, keyboard and mouse, pull the power cord and then clse the lib to my MacBook. I get home, open the lid and then find that the screen is stuck at maybe 5% brightness (so dark that I'd not noticed that it wasn't completely black the first few times). It's hard for me to tell if it went into this mode as it was suspending or as it was waking up from being suspended. As far as I can tell it's completely locked up. The very dim screen isn't showing any signs of activity, and the machine never makes any attempt to connect to the network so I can't ssh in and see if it's live in any way.

The only fix seems to be to push the power button and hold it in for several seconds until it switches off.

As far as I can tell there's no log of any crash, looking in console hasn't pointed me at anything. I've not really spent any time trying to reproduce this at home yet. It doesn't happen every time as it is.

Does anyone have any suggestions as to where to look or how to go about pinning this down any more?

Thanks - Guy