If you are willing to add a registry entry, you can set the following:
HKEY_CURRENT_USER\Software\Wolfram Research\Mathematica DisableKeypadEnter = DWORD:1 (DWORD is the type, not part of the value)
I dont have number pad so...
What kind of keyboard are you using? What OS are you using? Does it have additional Numpad Enter key? Do you use "sticky keys" feature? Also take look at this link
