Drag Source Sequence

Rod offers you already a lot of details. Do you want more than one attempt? Is this a scored D&D or not? You need the object actions if you want to show a feedback after having dragged one drag source. Another approach could be to use the InBuilt states that are available for both drag sources and drop targets. Are you aware of them?

Yes it is possible but it's not all that simple to achieve and you are somewhat limited in terms of how you let the user see that the order is not correct..

Basically, you need to set up Object Actions on the Target so that when any Drag Object is dropped on the target a Conditional Advanced Action is executed which checks whether or not this particular Drag Object is being placed on the Target in the correct order.

If the order IS correct, then no action would be taken.  However, if the order is incorrect, then a hidden feedback caption can be shown to tell the user this is not the correct order of placement.

However, at the moment these actions are generated, the Drag Object has already been placed on the Target. It would be nice if you had the option of causing the incorrectly placed Drag Object to be rejected by the Target, but that only possible if the Drag Object was NOT allowed to be placed on the Target, and in you case it's only the ORDER of placement that is incorrect.