Resolution:
In GridServer 3.2, when handling a Service invocation error, both getTaskInput() and getLastCause() return null.

getTaskInput() and getLastCause() are not supported for ServiceInvocationException in GridServer 3.2. This issue is resolved in GridServer 4.0, but ServiceInvocationException's class hierarchy is different in GridServer 4.0 such that getTaskInput() and getLastCause() are no longer available.

You may be able to achieve similar behavior by keeping a client-accessible copy of your Task inputs in an array or table that you can index using the Task ID (passed as the id argument to handleError()).