Maps Crashes with Javascript marker.setOptions ?

I am using a popular Wordpress plugin.. and associating my own "icon" for the "marker"...

Two days ago "marker.setOptions" gave me this error in the Firefox console...
is not a function .

Then it seemed to have corrected itself.. and was fine for a day or so.

And now again today it started again. I have only been working on this project for a week.

My "key" to access maps is all good.. my maps produce fine. It is just this marker.setOptions is not a function.
At the same time I also use...
map.setOptions({styles: styles}); and I have no problems.

My exact is marker.setOptions({'icon': myIcon });


I just don't under stand why marker.setOptions starts working and then crashes a day or so later with is not a function ?

If somebody can point me to a Google User group or something or comments on this it would be great.
Thanks again group.
Rob.