Argh, don't know a damn thing about VPS's I'm afraid. But my guess is that that's where the problem lies.
I'd check out the PHPSysInfo source and find out the commands it's trying to do and do them myself, see if they work. Just hunt down the problem, I'd guess that it's having trouble detectng your OS and therefore can't find out everything else (because RAM info is placed in different places on BSD and Linux for example), so maybe hard coding in your OS might do the trick. But I'm just guessing :-)