Problem getting into EV mode

Is the issue I'm describing below normal behavior, or hopefully something that can be fixed?

I have a 2009 Prius with an Enginer 4kwh battery pack. I know that the Prius' programming has a number of parameters that control when it will enter EV mode.

The display says "Cannot enter EV mode now" when engaging my Coastal EV mode switch at times when I believe it should be able to enter EV mode.

Here are the conditions from a recent trip:
Stopped at a light
The ICE not running
Car fully warmed up (just drove 10 miles)
AC off
Outside air temp 62 degrees
Battery showing green bars with the top bar white

If I enter EV mode when the car is started cold then it works fine. Once I've driven it a while I can't get it to return to EV mode reliably.

The last time I spoke with my local Toyota dealer they said that because the 2009 American Prius was not shipped with an EV mode switch they would not support that mode.

 

I just ordered a Scangauge. Looking forward to using it to troubleshoot.