You will experience this error if you’ve added a Delay Activity to your Workflow and you have an object in memory that is unable to be serialized when the workflow executes the DelayFor. The error isn’t really clear and nothing is written to the Event Log either when this error occurs.
If you have a class that you store information for your workflow ensure it is marked as [Serializable], if you have a property of your class that you don’t want/can’t serialize then mark it as [NonSerialized].
I had the same problem, even after I have marked my classes as [Serializable], the error is still there. Any help?
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It is quite possible you are trying to serialize an object that cannot be serialized, example if you try to persist an SPWeb or SPSite object this error can also happen.
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