Here's an excerpt from the WSDK 5.1 docs:
AXIS-based Web services and JSR109-based Web services?
The WSDK is based on JAX-RPC and JSR 109 and not on AXIS (Apache eXtensible Interaction System).
Although AXIS is based partly on JAX-RPC, it also supports other technologies,
such as *.jws (Java Web Service) files, and *.wsdd (Web Services Deployment
Descriptor) files, which are not supported by the WSDK.
Another difference between Web services that are based on AXIS and Web
services that are created using the WSDK is the manner in which they are
packaged. Furthermore, EAR files created for AXIS-based Web services will
not work with Web services created with WSDK.
If you have an AXIS-based application (including ones developed with WSDK
V1.0) that you would like to use on WSDK V5.1, the best approach is to
rewrap the application's business logic as a new Web service. The WSDK
provides an Eclipse IDE or command-line tools that allow you to do this,
or, if you prefer, you can create the Web service manually.
If your application logic or Web service client uses classes from the AXIS
API, you will not be able to use them on the WSDK V5.1 runtime.