Simple Custom Data Flow Transformation Doesn't Produce Any Output

I've built a simple custom data flow transformation component following the Hands On Lab (http://www.microsoft.com/downloads/details.aspx?familyid=1C2A7DD2-3EC3-4641-9407-A5A337BEA7D3&displaylang=en) and the Books Online (ms-help://MS.MSDNQTR.v80.en/MS.MSDN.v80/MS.SQL.v2005.en/dtsref9/html/adc70cc5-f79c-4bb6-8387-f0f2cdfaad11.htm and ms-help://MS.MSDNQTR.v80.en/MS.MSDN.v80/MS.SQL.v2005.en/dtsref9/html/b694d21f-9919-402d-9192-666c6449b0b7.htm).

All it is supposed to do is create an output column and set its value to the result of calling a web service method (the transformation is synchronous). Everything seems fine, but when I run the data flow task that contains it, it doesn't generate any output. The Visual Studio debugger displays it as yellow, with 1,385 rows going into it, but the data viewer attached to its output is empty. The output metadata looks just like I expect: all of my input columns plus the new column, correctly typed. No validation or run-time warnings or errors are reported.

I'll include the entire C# file below, which only overrrides the ProvideComponentProperties, Validate, PreExecute, ProcessInput, and PostExecute methods of the parent PipelineComponent class.

Since this is effectively a specialization of the DerivedColumn transformation, could I inherit from the class that implements the DC component instead of PipelineComponent? How do I even find out what that class is?

Thanks! Here's the code:
using System;
// using System.Collections.Generic;
// using System.Text;

using Microsoft.SqlServer.Dts.Pipeline;
using Microsoft.SqlServer.Dts.Pipeline.Wrapper;
using Microsoft.SqlServer.Dts.Runtime.Wrapper;

namespace CustomComponents
{
[DtsPipelineComponent(DisplayName = "GID", ComponentType = ComponentType.Transform)]
public class GidComponent : PipelineComponent
{
///
/// Column indexes for faster processing.
///
private int[] inputColumnBufferIndex;
private int outputColumnBufferIndex;

///
/// The GID web service.
///
private GID.WS_PDF.PDFProcessService gidService = null;

///
/// Called to initialize/reset the component.
///
public override void ProvideComponentProperties()
{
base.ProvideComponentProperties();
// Remove any existing metadata:
base.RemoveAllInputsOutputsAndCustomProperties();
// Create the input and the output:
IDTSInput90 input = this.ComponentMetaData.InputCollection.New();
input.Name = "Input";
IDTSOutput90 output = this.ComponentMetaData.OutputCollection.New();
output.Name = "Output";
// The output is synchronous with the input:
output.SynchronousInputID = input.ID;
// Create the GID output column (16-character Unicode string):
IDTSOutputColumn90 outputColumn = output.OutputColumnCollection.New();
outputColumn.Name = "GID";
outputColumn.SetDataTypeProperties(Microsoft.SqlServer.Dts.Runtime.Wrapper.DataType.DT_WSTR, 16, 0, 0, 0);
}

///
/// Only 1 input and 1 output with 1 column is supported.
///
///
public override DTSValidationStatus Validate()
{
bool cancel = false;
DTSValidationStatus status = base.Validate();
if (status == DTSValidationStatus.VS_ISVALID)
{
// The input and output are created above and should be exactly as specified
// (unless someone manually edited the persisted XML):
if (ComponentMetaData.InputCollection.Count != 1)
{
this.ComponentMetaData.FireError(0, ComponentMetaData.Name,
"Invalid metadata: component accepts 1 Input.",
string.Empty, 0, out cancel);
status = DTSValidationStatus.VS_ISCORRUPT;
}
else if (ComponentMetaData.OutputCollection.Count != 1)
{
this.ComponentMetaData.FireError(0, ComponentMetaData.Name,
"Invalid metadata: component provides 1 Output.",
string.Empty, 0, out cancel);
status = DTSValidationStatus.VS_ISCORRUPT;
}
else if (ComponentMetaData.OutputCollection[0].OutputColumnCollection.Count != 1)
{
this.ComponentMetaData.FireError(0, ComponentMetaData.Name,
"Invalid metadata: component Output must be 1 column.",
string.Empty, 0, out cancel);
status = DTSValidationStatus.VS_ISCORRUPT;
}
// And the output column should be a Unicode string:
else if ((ComponentMetaData.OutputCollection[0].OutputColumnCollection[0].DataType != DataType.DT_WSTR) ||
(ComponentMetaData.OutputCollection[0].OutputColumnCollection[0].Length != 16))
{
ComponentMetaData.FireError(0, ComponentMetaData.Name,
"Invalid metadata: component Output column data type must be (DT_WSTR, 16).",
string.Empty, 0, out cancel);
status = DTSValidationStatus.VS_ISBROKEN;
}
}
return status;
}

///
/// Called before executing, to cache the buffer column indexes.
///
public override void PreExecute()
{
base.PreExecute();
// Get the index of each input column in the buffer:
IDTSInput90 input = ComponentMetaData.InputCollection[0];
inputColumnBufferIndex = new int[input.InputColumnCollection.Count];
for (int col = 0; col < input.InputColumnCollection.Count; col++)
{
inputColumnBufferIndex[col] = BufferManager.FindColumnByLineageID(input.Buffer, input.InputColumnCollection[col].LineageID);
}
// Get the index of the output column in the buffer:
IDTSOutput90 output = ComponentMetaData.OutputCollection[0];
outputColumnBufferIndex = BufferManager.FindColumnByLineageID(input.Buffer, output.OutputColumnCollection[0].LineageID);
// Get the GID web service:
gidService = new GID.WS_PDF.PDFProcessService();
}

///
/// Called to process the buffer:
/// Get a new GID and save it in the output column.
///
///
///
public override void ProcessInput(int inputID, PipelineBuffer buffer)
{
if (! buffer.EndOfRowset)
{
try
{
while (buffer.NextRow())
{
// Set the output column value to a new GID:
buffer.SetString(outputColumnBufferIndex, gidService.getGID());
}
}
catch (System.Exception ex)
{
bool cancel = false;
ComponentMetaData.FireError(0, ComponentMetaData.Name, ex.Message, string.Empty, 0, out cancel);
throw new Exception("Could not process input buffer.");
}
}
}

///
/// Called after executing, to clean up.
///
public override void PostExecute()
{
base.PostExecute();
// Resign from the GID service:
gidService = null;
}
}
}