If you are receiving this error when validating your RFID process and don't know why, or you have never seen this error before, read on as it just might save you some pain...
RFID Processes - 101 
RFID Processes consist of device bindings and component bindings. The device bindings link physical RFID devices to logical devices. Component bindings define the event handlers that perform the processing. Conceptually, an RFID process looks something like this:
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Source: Microsoft BizTalk RFID Online Help
When PhysicalDevice1 raises an event, it is sent via LogicalDevice1 to EventHandler1 for processing. EventHandler1 processes the event and passes the event data to EventHandler2. Event handlers can also terminate the event processing and not pass the event on. (but lets leave that for another post)
When we put together RFID Processes that consist of multiple event handlers, we need to ensure that each event handler in the process can accept the event(s) passed from the previous one.
Back to the Problem
BizTalk RFID will throw "The process has a component that is not reachable..." error when it determines that an event handler in the process can not receive an event.
This can happen in two ways:
- The device binding is not set and the event can not reach the first event handler.
- An event handler can not pass an event(s) to the next event handler in the pipeline.
And it is this last case that can cause the pain.
A Common Scenario
You have a RFID process with two event handlers. The OOTB SqlServerSink event handler (EH1) and a custom event handler (EH2). BizTalk RFID throws the above error when you try to save. Why?..
In this case the first event handler, SqlServerSink, is not designed to pass on events. It's event handler method has no output parameter. (check out the method signatures PostEventToSink and PostEventsToSink in online help) Event processing will always stop at the SqlServerSink component.
The solution: Move the custom event handler (EH2) ahead of the SqlServerSink (EH1) event handler to pass validation.
An Actual Scenario (that resulted in much loss of sleep)
I had a RFID process that used the OOTB event handler RuleEnginePolicyExecutor to call BRE policies from the process. The next event handler in the pipeline was my custom component that I had used in many processes before with no issue. The output type of the RuleEnginePolicyExecutor event handler method(s) is RfidEventBase[]. The event handler method on my custom component only accepted RfidEventBase as an input parameter. That is, the RuleEnginePolicyExecutor component was passing my custom component an array of events and I only supported a single event in my event handler.
The solution: Create another event handler method that accepts RfidEventBase[] as the input parameter. I iterated through the array calling my original event handler method. Now my component supports both scenarios.
Troubleshooting
So when you receive this error, examine the message to identify the component at fault. Check the event handler method signatures of this and the previous component. What you are looking for:
- The previous event handler passes on the event (i.e. has an output parameter)
- The event handler at fault can accept the event (i.e. has an input parameter type that matches the event type sent)
As event handlers can have more than one event handler method, ensure that the event handler at fault has an event handler method with the right input type for each of the output types of the previous component. This becomes quite complex when we consider pipelines mat contain multiple logical sources as well.
Tip: The Custom Event Handler Project Template that shipped with the SDK Samples only implements event handlers that accept TagReadEvent and TagListEvent input types. You will need to implement another event handler that accepts RfidEventBase[] as an input type to use your component with the RuleEnginePolicyExecutor component.