This is because the given WSDL is using 'encoded' which is a RPC encoding and a very old way of doing things.
RPC encoding is not supported by wsimport
Some more info on your error message
As an alternative try use Apache Axis which is yucky and old, but I guess it will get you going.
For a Maven project, drop your WSDL in src/main/resources/wsdl
And add the following to your pom.xml
<dependency>
<groupId>org.apache.axis</groupId>
<artifactId>axis</artifactId>
<version>1.4</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.apache.axis</groupId>
<artifactId>axis-jaxrpc</artifactId>
<version>1.4</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>wsdl4j</groupId>
<artifactId>wsdl4j</artifactId>
<version>1.6.2</version>
<scope>compile</scope>
</dependency>
<plugins>
...
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>axistools-maven-plugin</artifactId>
<version>1.4</version>
<executions>
<execution>
<goals>
<goal>wsdl2java</goal>
</goals>
</execution>
</executions>
<configuration>
<packageSpace>com.mycompany.service.client</packageSpace>
<sourceDirectory>src/main/resources/wsdl</sourceDirectory>
<outputDirectory>target/generated-sources/wsdl2java</outputDirectory>
</configuration>
</plugin>