I get that (in 4.3) when trying to open a task for which input data set(s) have not yet been created. Are you trying to open tasks before running the entire process flow up to that point? It doesn't sound like it, based on your description of creating new tasks, but that's my experience with that error and maybe there's something you're doing that is related (is it when you create the tasks, or when you run the tasks afterwards)? Does it matter if you run the entire process/project or if you run them one at a time?
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