If you are using any frameworks other than the Apple-provided WebObjects frameworks that include client-side classes, you will need to manually copy the framework's client-side .jar files into your project's WebServerResources/Java directory (and remember to always update them) or have Ant automatically copy them there when building/installing by modifying the build.xml and javaclientbuild.xml files to go grab all the client-side jar files from the local frameworks directory (Usually /Library/Frameworks) using the following addition:
Either way, you will also need to add an entry to the project's ClasspathClient.txt file for each one.
WebObjects seems to be able to find its own client-side classes from within the Library/Frameworks directory, but it cannot find any others.
For example, I have a framework named MyFoundation.framework that has a couple classes in it that are used by the client-side of my application. In order for WO to find these classes, they must be in a Jar located in the MyApp.woa/Contents/WebServerResources/Java/. You will then need to make sure that the ClasspathClient.txt classpath file has an entry pointing to it like so:
You can also