This is a SharePoint Designer 2010 error I came across afterI copied the OOTB Feedback workflow and butchered it to within an inch on its life. Understandable really. I had removed all the Initiation Form Parameters and had created some of my own. The workflow was not highlighting any activties in red so I could not locate where this error was coming from.
I thought I had set all the necessary OOTB workflow variables with blank or reasonable values but somehow I missed one- DurationUnit. Actually, I think I had set it in a workflow activity to: Days. It didn’t complain unfortunately but it was actually expecting: Day(s).
Anyway, the point of the story is that the Advanced Properties button on the workflow ribbon saved the day. Click him and you will see all the core workflow avriables layed out for you.
I found the DurationUnit variable which had not been set correctly, set it using the vairbale value drop down and saved the workflow. Then it deployed and I released my frankenstein workflow creation to do its evil job! Muwahahaha