I have a number of Sequential Workflows that I created. Given they all used the same base group of methods I created a new base SequentialWorkflowActivity for my Sequential Workflows to inherit from. As soon as I do this though, I can no longer open the workflows in the designer and am given the following error:

The designer could not be shown for this file because none of the classes within it can be designed. The designer inspected the following classes in the file:
WorkflowName. The base class WorkflowName could not be loaded. Ensure the assembly has been referenced and that all projects have been built.

My custom SequentialWorkflowActivity can be opened in the designer, but any workflows that inherit from it cannot.

All files are in a single project in the solution.

Any ideas how to make the workflows editable in the designer? Do I need to implement more methods/properties in my SequentialWorkflowActivity to be able to do so?

  • it appears that my machine was out of memory :)
    – Mauro
    Jan 10, 2014 at 10:57

1 Answer 1


It appears that my Virtual Machine was running low on memory and stopping the designer from being opened correctly. Restarting the VM allowed this to work correctly.

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