Well I am going to be the one who mentions the obvious.
Try putting your keyboard in direct line-of-sight of the receiver and see if it gets any better. Try placing the receiver a little higher than it is currently located or a little lower, also try putting the receiver right next to the keyboard
Are there any other wireless devices around (routers, network cards, mobile phones etc.) operating near it? If so try switching them off and then test.
This should either fix it or rule out the fact that its a signal issue.
After this it is likely that it is a software issue. Have you installed all the Logitec keyboard/mouse software? (not just the drivers, but the actual tweeking software)? Are there any new versions available? if so try updating them.
Unsolved 
