Obviously this is because I have accidently assigned an cable attribute to something other than a wire and/or have deleted a wire but an attribute was left behind. Is there some method for finding these and removing them from the drawing.

One way would be to go to the Report tab (bottom of the main drawing window).  This lists all attributes in all objects so you should be able to select the row corresponding to an erroneous Attribute value.  You can either delete the value by doubleclicking on the cell, or go back to the Plot tab (the main drawing) where the object will be selected and edit it there.

I hope this is helpful.