Workflow expression "cannot find symbol" of compiled custom class

Version: Windchill 13.0

Use Case: I wrote/compiled some code to collect and send to a messaging queue a part BOM. Part of this code has two custom classes (BOM, BOMLines). The return of my method is a List but the workflow expression says it "cannot find symbol" for my BOM class.

Description:

In the workflow expression I have:

java.util.List<ext.comp.BOM> myBOM = ext.comp.getBOMSfromECN(cn);
ext.comp.Messages.sendToERP("BOM from ECN: " + myBom.toString());		

Check syntax in the workflow doesn't like the ext.comp.BOM...

WfExpression_88956210.java:72: error: cannot find symbol
 java.util.List<ext.ursa.BOM> myBOM = ext.ursa.getBOMSfromECN(cn);
 ^

On the server I have a BOM.java and BOM.class. Originally I had both of my custom classes in my main code but a compilation error said these would have to exist as standalone .java, so they do. 

How can I use my custom class in a workflow expression? 

package ext.comp;

import java.util.*;

public class BOM {
 private List<BOMLine> lines;
 private String parentPN;
 private String parentRev;

 public BOM(List<BOMLine> lines, String parentPN, String parentRev) {
 this.lines = lines;
 this.parentPN = parentPN;
 this.parentRev = parentRev;
 }
 
 public void setLines(List<BOMLine> children){
 this.lines = children;
 }
}