So I figured out what my issue was and it's all ok now ... but thought i'd throw in the issue here for devs.

Here is a bunch of text, blah blah blah
--------------------
[call - to a table]
Here is a Title

Above is a sample of what was in my story template, formatting exactly the same, and with that I would get the subject line error message off and on. Not 100% of the time, it was sporadic.

So stepping through the story template I finally worked out that if the [call - to a table] was bold I'd get the error, if i removed the bold then it worked properly.

Anyway ... just thought i'd let it be known.