Hello all.
I have managed to get this to work. Here is a close up of the diagram
I have used the an extended properties table (switchtable with field nerrors) to hold the output value identifiedErrors from the EvaluateDataQuality. I have left the output as visible. This lets me change the stored value containing the number of identified errors. There are 3 paths out of the Update Job Properties step. The leftmost is triggered when the Update Job properties fails.
The rightmost leading back to the editor for when there are errors has the expression:
Boolean(jobExtendedProperty($job, 'switchtable', 'nerrors') > 0)
The middle path leading on to a Reconcile and Post step when there are No Errors has the expression:
Boolean(!jobExtendedProperty($job, 'switchtable', 'nerrors') > 0)
i.e. the NOT of the other expression.
This works but
Boolean(jobExtendedProperty($job, 'switchtable', 'nerrors') == 0)
does not with a message saying there is no path.
Hope this help some-one else