portal service getting "null" after server restart & sometimes randomly

Hi,

We have a portal service running on our portal. It's a simple portal service exposing a few methods.

Everything works fine when i deployed the dc [_DC Type_: Portal application standalone (Packed in SDA) ].

1) But if the server is restarted, and we try to access this portal service, we get NULL exception. It works fine if re-deploy DC again.

2) And sometimes, this occurs even if the server isn't restarted.

I have given startup property in the portalapp.xml

Plz find below the portalapp.xml

<?xml version="1.0" encoding="UTF-8"?>
<application>
  <application-config>
    <property name="SharingReference" value="com.sap.portal.compatibility50.cache"/>
    <property name="startup" value="true"/>
    <property name="PrivateSharingReference" value="com.sap.portal.ivs.connectorservice"/>
  </application-config>
  <components/>
  <services>
    <service name="MyDataService">
      <service-config>
        <property name="className" value="com.pkg1.MyDataService"/>
        <property name="startup" value="true"/>
      </service-config>
...
...
    </service>
  </services>
</application>

It would be great if anyone can help!

Thank you.

SK.