Java HotSpot Virtual Machine

Hello,

I'm trying to launch my java web start application in a windows 7 64-bit machine (8 GB RAM) with the parameter -Xmx4g in the JNLP file (java version 1.6.0_27). I get the error "Could not create the Java Virtual Machine". When I reduce it to -Xmx1000m it launches fine but at some point my application crashes because of java.lang.OutOfMemoryError. When I run the jar file java -jar -Xmx4g MyApplication.jar from the command line it runs fine and never crashes.

The same application can be launched in windows XP SP3 (2GB RAM) with -Xmx1000m (java version 1.6.0_26) and never crashes.

So basically what I've concluded is that in the 64-bit my application runs out of memory (even though it works fine for the same dataset in the 32-bit) but I cannot find a way to address the extra memory I need from the JNLP file without having the error "Could not create the Java Virtual Machine".

I'm not sure if there is an obvious solution that I'm missing, I've looked online but I'm no wiser. I would appreciate any help!

Thanks,
Laura