If you've built a custom SmartObject  (a SQL Azure SmartObject for example) you may want to use it within the context of a workflow. In this example I have made a SmartObject called 'Test SMO' and you will see in the image that it is not available for use:

To fix this we need to go locate and edit our target SmartObject. Selct the 'General' tab and ensure the 'Allow this SmartObject to be used in WorkFlows' is checked:

After checking that option, the SMO will appear in the context of designing a workflow: