Java HotSpot Virtual Machine

Hi every body.
Does someone know the meaning of this error?

java.io.IOException: CreateProcess: prueba error=2
at java.lang.Win32Process.create(Native Method)
at java.lang.Win32Process.<init>(Win32Process.java:63)
at java.lang.Runtime.execInternal(Native Method)
at java.lang.Runtime.exec(Runtime.java:566)
at java.lang.Runtime.exec(Runtime.java:428)
at java.lang.Runtime.exec(Runtime.java:364)
at java.lang.Runtime.exec(Runtime.java:326)
at org.apache.jsp.ChangeDirBajaRCXX_jsp._jspService(ChangeDirBaja
p.java:185)....................................

.....................................................

It's the result of this code:
cmd="prueba.bat";
exec(cmd);

and the prueba.bat is really simple:
@echo off
lejos HelloWorld

'lejos' is an exe file.

If i try 'lejos HelloWorld' from the MS-DOS it runs ok.

Thanks!!