Steps to reproduce it:

1. Create a sample Synchronous Sample project SynchronousSample.
2. Create an empty XSLT module project XSLTModule.
3. Add "SynchronousSample" project as one of "Project References" to XSLTModule project 
  (if you need the instruction for this step, let me know).
4. Create a new wsdl file in XSLTModule: 
    1) Accept default settings, click "Next" in the "Name and Location" panel.  
    2) Modify the "Element Or Type" field of Input message part from "xsd:string" to "ns:typeA". The typeA
       is defined in SynchronousSample.xsd (Select "By File -> SynchronousSample.xsd -> Elements -> typeA" in "Select
Element Or Type" dialog.
    3) Modify the "Element Or Type" field of Output message part from "xsd:string" to "ns:typeA".
    4) Click "Finish".
5. Create a new Composite Application CompositeApp.
6. Edit Application Configuration. Drag and drop "XSLTModule" to the JBI Module area in CASA Editor.
7. Build.
Will et the following error:
C:\Users\Hong\Documents\NetBeansProjects\SynchronousSample\SynchronousSample\nbproject\build-impl.xml:156: 
Found validation errors:
Error: In part "inputMsg", attribute element's value "ns:typeA" is not a valid xml schema element available in this wsdl
file. : Specify a valid schema element value for element attribute.
Error: In part "greeting", attribute element's value "ns:typeA" is not a valid xml schema element available in this wsdl
file. : Specify a valid schema element value for element attribute.
BUILD FAILED (total time: 0 seconds)

XSLT doesn't support this cross project XML file reference use case.