I've asked the question several times in various forums. Nobody has yet answered the question.

The most complete answer was from Randy, but did not define how INAVerr is calculated and why 255 is bad, only that it may be a problem in my logs.

It has to do with GPS and Pixhawk data communication. I have a CSGShop Neo-M8N GPS w/compass and contacted them concerning INAVerr. They say it is a Pixhawk issue; no help there.

Here are the relevant threads:

This was the first thread I started due to odd behavior (which may not be connected to this) of my copter and subsequent log analysis. I didn't know what the errors meant using Auto Analysis and Flight Log Analyzer. 

http://diydrones.com/forum/topics/csgshop-neo-m8n-is-giving-pm-errors

Randy's last response:

DG,

I should be more clear.  The PM message's long-loops error is a red-herring.  The inav errors are likely a real problem. I don't know why in your logs it keeps having problems.  Rob apparently looked at your logs and the GPS seems to be updating at the correct rate.

The latest thread drew a few others in with the same issue.

http://diydrones.com/forum/topics/inaverr-is-it-the-gps-or-fc-or-neither

Got it. The long loop errors are not a problem, but the INAVerr is likely to be a problem, but what does that mean?

So the quest continues. There are others reporting the same "problem" (if it really is), but thus far it has been a dead end determining what it all means and if there is a risk of a mechanical malfunction caused by these INAVerr data. I really don't want nor can afford to wreck my copter. QED

If anyone has some insight concerning this, by all means please speak up.