Why java Runtime.exec("rasdial.exe MyVPN login pwd") freezes Win2003 server 64 ?

[Manuel Elias]

I have three PC :

PC1 : WinXP Pro
PC2 : Win2003 Server x64
PC3 : Win 7 x64

PC1 & PC2 can connect to PC3 via a VPN (PPTP) using windows menu to launch a configured VPN connection MyPVN.

PC1 & PC2 can connect to PC3 using console command :
"rasdial.ex e MyVPN login password"

But ...

...PC1 only could achieve the VPN connection via java
( version 1.4.2 or 1.6 that's doesn't matter ).
In my java app, I use

Runtime.exe("cmd.exe /c MyVPN login password");

to achieve the VPN connection on PC1, but...

...when trying that from PC2 the result is a system freeze !

The only way to unfreez PC2 is to close VPN connection on PC3 !

It's crazy and I need this to run on PC2 as a part of my job !

Some suggestions would be appreciated,

Thank you for your help.