I suspect you have some tab caching / merging going on in your flavor... according to my experience that's the reason for the "Step *..." message. Tab caching gets somehow confused and doesn't find a field a step is referring to.
Unfortunately in such cases I had to redesign my flavor and change the way the tabs were merged.
I don't have an exact answer to what the problem is in your case but I'd suspect if you deactivated tab caching, this error wouldn't happen.