Unable to run wsimport on wsdl

I'm trying to import the wsdl using Java's wsimport, however its throwing up some errors. Any idea what the cause might be? Is the wsdl definitely valid?

C:\Java\workspace\buildmaster-plugin>%JAVA_HOME%\bin\wsimport wsdl\BuildMaster.wsdl
parsing WSDL...


[WARNING] src-resolve.4.2: Error resolving component 's:schema'. It was detected that 's:schema' is in
 namespace 'http://www.w3.org/2001/XMLSchema', but components from this namespace are not referenceable 
 from schema document 'file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl#types?schema1'. 
 If this is the incorrect namespace, perhaps the prefix of 's:schema' needs to be changed. If this is the 
 correct namespace, then an appropriate 'import' tag should be added to 
 'file:/C:/Java/workspace/buildmasterplugin/wsdl/BuildMaster.wsdl#types?schema1'.
  line 128 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl#types?schema1

[WARNING] src-resolve: Cannot resolve the name 's:schema' to a(n) 'element declaration' component.
  line 128 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl#types?schema1

[ERROR] undefined element declaration 's:schema'
  line 128 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl

[ERROR] undefined element declaration 's:schema'
  line 150 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl

[ERROR] undefined element declaration 's:schema'
  line 172 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl

[ERROR] undefined element declaration 's:schema'
  line 217 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl

# [ERROR] undefined element declaration 's:schema'  
  line 455 of file:/C:/Java/workspace/buildmaster-plugin/wsdl/BuildMaster.wsdl #

etc

Product: BuildMaster
Version: 4.5.6

I'm not sure what the tool is validating exactly, but after uploading the WSDL file to https://www.wsdl-analyzer.com, it said the document was valid.

I am not super familiar with Java or any Java tools, but the same problem looks like it has occurred here: http://stackoverflow.com/questions/13499860/jax-ws-error-on-wsdl-file-error-resolving-component-sschema