Why Am I getting a violation in dependency message?

[Alex Eldridge]

I have a portfolio plan in v 2.18 server.  I set a dependency so that epic A blocks epic B.  I expected to see B scheduled after A, but instead B failed to appear in the schedule.  When I clicked it in scope I see a message: 'Violation in dependency.  A required work item could not be scheduled". 

can anyone say what is causing this?  I have another plan where dependencies work.  The only difference I can see at this point is that in the plan where they don't work I have added multiple sub items within estimates for different expertise, eg .NET, front end, QA, project mgmt.   Both plans use hours as the unit for measuring level of effort.

[Clare]

Hi Alex,

Most likely there is some reason why the required issue (Epic A) cannot be scheduled, and Epic B cannot be scheduled because it depends on A. Clicking on the Epic A in the scope view should help you to identify what the problem is.