Agreed that a better error message is needed.
So, the problem was NOT that the month and year were invalid, it just didn't like the fact that I used an automated way to provide it (e.g. RoboForm or Cut and Paste).
A message like "please select month and year again but actually clicking the drop down box entry" would have been better -- or simpler yet: "as an added security measure, please select your month and year choices again".
The way it works now makes it seem like the page is broken, and that does not instill confidence.
Oh well, in my case it is probably a "moot point" until my membership comes up for renewal again. Plenty of time to implement an improvement.