Which OS are you running?
There is an old problem that I remember from Windows 2000 in which all kinds of computers would give errors concerning keyboard drivers when the end user attempted a standby or hibernate operation. Most of these errors, as I recall, were traced back to ATM (Adobe Type Manager). It was installing a process which "hooked" the keyboard driver. When the driver tried to do its standby or hibernate thing, the hook wouldn't allow it. ATM is not the only software that did this. Any keyboard state "watcher" (like some spy programs, for instance) might have the same effect.
If this isn't helpful, maybe you could post back with the exact contents of the error messages, and also let us know the OS and the names of concurrent processes running on the machine when this happens.
- Collin