ant tasks on WSAD 5.1

Hi all,
I'm trying to run ant tasks(start/stop app, list etc.,) through an ant build
file.
I get the following error : 
"  [wsadmin] WASX7023E: Error creating "SOAP" connection to host
"localhost"; exception information: [SOAPException:
faultCode=SOAP-ENV:Client; msg=javax.management.ObjectName; local class
incompatible: stream classdesc serialVersionUID = -5467795090068647408, local
class serialVersionUID = 1081892073854801359;
targetException=java.lang.IllegalArgumentException: javax.management.ObjectName;
local class incompatible: stream classdesc serialVersionUID =
-5467795090068647408, local class serialVersionUID = 1081892073854801359] 
[wsadmin] WASX7213I: This scripting client is not connected to a server process;
please refer to the log file D:\IBM\WebSphere Studio\Application
Developer\v5.1.2\runtimes\base_v51\logs\wsadmin.traceout for additional
information.  [wsadmin] WASX7022E: Problem running command "$AdminApp
list" -- exception information: com.ibm.ws.scripting.ScriptingException:
WASX7206W: The application management service is not running. Application
management commands will not run."

SOAP port is the same in wsadmin.properties and System.out.
Now i try running wsadmin from the was.home/bin and it works fine.