“Error occurred during initialization of VM; Could not reserve enough space for object heap” using -Xmx3G

Could it be that you’re using a 32-bit jvm on that machine?

Here is how to fix it:
Go to Start->Control Panel->System->Advanced(tab)->Environment Variables->System
Variables->New:
Variable name: _JAVA_OPTIONS
Variable value: -Xmx512M

Variable name: Path
Variable value: ;C:Program FilesJavajre6bin;F:JDKbin;

Change this to your appropriate path.