The upgrade resulted from upgrading to ubuntu 8.04 ... which automatically upgraded Gramps too - how efficaciously I can't be sure.
That said there is only one file called NarrativeWeb.py in the plugins folder. Although there is another file called NarrativeWeb.py.save also there - provenance unknown.
For what it's worth I have subsequently verified that the problem was more particularly that Gramps was not re-generating the img files for Source gallery images on the Source pages. The Individual Gallery images seem to be just fine.
Could it be that my NarrativeWeb.py file is somehow corrupted? Perhaps if someone could direct me to a known good one - or send it to me - that would be worth trying?