You cannot <exec> a .bat file. You need to <exec> cmd.exe instead. Please see 
the FAQ. --DD

You can execute a batch file by specifying vmlauncher="false".  On Windows, this
will cause the executable to be run through cmd.exe.

You can exec a batch file.   
You can use vmlauncher="false" but you don't need to if you give the full file   
name (i.e. include the .bat and the full path).    
  
What you cannot do is try and execute "${jwsdp.home}\bin\xrpcc.bat". I'd 
suggest you look at why jwsdp.home is not set to a value.  

I set the correct value to jwsdp.home and checked the full path definition is 
actually expressed (xrpcc.bat) but the problem persists. Here is the complete 
diagnostic message indicating the fault:
compile-server:
     [echo] Compiling the server-side source code....
    [javac] com\web_tomorrow\xmlrpctut\InterestImpl.java omitted as 
com/web_tomorrow/xmlrpctut/InterestImpl.class is up to date.

xrpcc-server:
     [echo] Running xrpcc for the server:
     [exec] Current OS is Windows 2000
     [exec] Executing '\Documents and Settings\Administrator\jwsdp-1.1
\bin\xrpcc.bat' with arguments:
     [exec] '-classpath'
     [exec] 'build/server:build/shared'
     [exec] '-server'
     [exec] '-d'
     [exec] 'build/server'
     [exec] 'config.xml'
     [exec] 
     [exec] The ' characters around the executable and arguments are
     [exec] not part of the command.

BUILD FAILED
file:C:/Documents and 
Settings/administrator/mysunprojs/interest_ws/build.xml:64: Execute failed: 
java.io.IOException: CreateProcess: "\Documents and 
Settings\Administrator\jwsdp-1.1\bin\xrpcc.bat" -classpath 
build/server:build/shared -server -d build/server config.xml error=2
	at org.apache.tools.ant.taskdefs.ExecTask.runExec(ExecTask.java:371)
	at org.apache.tools.ant.taskdefs.ExecTask.execute(ExecTask.java:250)
	at org.apache.tools.ant.Task.perform(Task.java:341)
	at org.apache.tools.ant.Target.execute(Target.java:309)
	at org.apache.tools.ant.Target.performTasks(Target.java:336)
	at org.apache.tools.ant.Project.executeTarget(Project.java:1339)
	at org.apache.tools.ant.Project.executeTargets(Project.java:1255)
	at org.apache.tools.ant.Main.runBuild(Main.java:609)
	at org.apache.tools.ant.Main.start(Main.java:196)
	at org.apache.tools.ant.Main.main(Main.java:235)
Caused by: java.io.IOException: CreateProcess: "\Documents and 
Settings\Administrator\jwsdp-1.1\bin\xrpcc.bat" -classpath 
build/server:build/shared -server -d build/server config.xml error=2
	at java.lang.Win32Process.create(Native Method)

could you add a build file snippet and your batch file xrpcc
I have tried to execute a batch file located under "Dokumente Und 
Einstellungen" with the cvs head version of ant and it works.
Can you try with ant1.5.2 and with a nightly build to see if it makes any 
difference ?

oops.. sorry for having overlooked the path included in the build file to 
access xrpcc.bat. Problem solved: the path was wrong as it did not point to the 
actual place where xrpcc.bat was located. Thanks to all those who adreesed me 
to the right direction to watch (namely levylambert@tiscali-dsl.de).