Hi, I am attempting to model a worklfow using a "WCF Workflow Service" in .net / vs 2010 that needs to handle out of order execution gracefully (but not allow it - if thath makes sense!?)

For example I have 2 receive activities one called Initialize and the other called GetValue inside a FlowChart.

In most cases Initialize should be called first and GetValue after (as modled in the flow chart).

However if GetValue is executed before Initialize I do not want to return an "out of order" exception (although when I look at the WCF test client, I can't actually see an exception). But instead a custom exception saying something like "you must initialize first".

In theory I could model this with lots of parallel activities and conditions to check if Initialized / Running / Terminated etc. But the business process I am modelling if very very similar to a state machine... except it must handle people executing things in the wrong order.

Ideally I would like to catch the "out of order" exception (thought I don't think it's really an exception as such), check the 'exception' to see which function was attempted to run and then handle it.

I have done some research around enabling AllowBufferedReceive. However I don't want to be able to execute out of order (I don't think), but instead give a detailed response if it does happen.

I've looked at the new beta state machine template for WF 4 - but i'm not sure if it does what i'm after?

I'm not sure if I have the wrong end of the stick, so any help would be greatly appreciated.

[EDIT] To help clarify...

Sorry it's a tricky one to explain.

The standard I am trying to implement (the e-learning standard SCORM RTE) is structured like a state machine i.e. certain functions can only be executed in certain states.

However the standard specifies that if the calling clients tries to execute a function that it is not meant to, then a warning should be issued... for example "you cannot use GetValue(), because you have not yet Initialized".

Ideally I'd like to structure the workflow as the theoretical state machine and not need to have to use multiple if/else's to handle all the scenarios where something could be executed out-of-order. I'd like to catch a out-of-order exception (but I don't think there is such an exception - as it's not in the debugger) and rethrow it.