Exception in WebService called through WDJ

I am in learning phase of BPM. I successfully created a process which involved 3 WDJ screens and 2level BPM process.

Although i faced below WebService Exception frequently

Exception on execution of web service  with operation Operation' in interface WSDL

Mainly I found two reasons for the exception:

1. Authentication has failed for webService

2. All the parameters are not set

Solution:

1. Set UserId Password to the web service to code

Refer link below:

http://wiki.scn.sap.com/wiki/display/WDJava/Exception+on+Execution+of+Web+Service

Or

Set Authentication Property to your WDJ application:

Select Application -> go to Property ->

Select Application Properties

Click Add

Click on browse select Authentication.

And Run the application. It will ask for credentials.

2.  If any of the parameter value is not set it might throw exception. If you dont have values for all set empty string.