Are the users using ad-block in FF and/or have the pop-up blocker enabled? What extensions/add ons do they have?

I did some research and from what I'm finding there are quite a few different reasons this could be occurring with drastically different solutions to each one.

The most likely cause is something in the browser setup. I haven't seen this error and I use Firefox exclusively so it's probably something specific to the setups of the users getting the error.

 I use Chrome and I do get this error when using PMs.

I think I do have some built in ad-blocker, but I haven't done anything special with the setup.

I've been able to work around this so far, but I would appreciate a fix.

I use Firefox, no addins aside from the default ones and it randomly appears for me. Last night when it happened, I switched to Chrome and the problem vanished.

Most of what I'm finding on this issue is saying it's browser related in some way. I'll keep looking into it but without being able to recreate the problem I don't have much to go on.

I don't have add blocker, but I do have the check mark box clicked for blocking pop ups.

For me, it's sporadic as well.  Sometimes it works fine and other times I get the error.

Wish I had more information.  As I discover more, I'll post it here.

Thanks for looking into it. 

This is just a shot in the dark, but could it have something to do with the URL?

I know that a number of the links seem to arbitrarily use either "nextgenrpg.com" or "www.nextgenrpg.com." I've seen some weird behavior from that.

That could have something to do with it. I finally got one of those errors today so I was able to get the whole error message and I was thinking along the same lines. Tracking down which one is a problem, if that's the case, is going to be time consuming.

Most of what's in Drupal's support for the problem is saying it's in the browser. After actually seeing the error message I don't think that's the case.

I think I found the problem causing this error. Everyone will have to log in again but autocomplete should now be working correctly. The fix should have also fixed the problem some people have had with staying logged in.

Just found out this may have also solved the problem some people were having with subscriptions not working properly.

Hip! Hip!  Horray!!

I was cued to log in when I came to the site, and did so.  So I will keep my eyes open and see if it has fixed all of the problems.

This is huge!  Thank you. 

What was the culprit?

*happy dances*

A setting in one of the drupal configuration files.

That particular error can be caused by a number of different things and is not specific to Drupal. Almost everything I was finding on it in my searches indicated it was either a slow connection or a browser issue. Neither of which could have been fixed at our end without hacking a core Drupal file. Which is not a good idea as it can break other things.

I finally found the suggestion to comment out certain lines in the settings file. With the switch in servers the new setup didn't need those lines and it was causing Drupal to get confused on where to look for the information.

Well, hopefully this will take care of all of those bizarre issues, that were affecting some but not others. It was very frustrating when things were working for most the members, but not all of them.

I figured it was somehow related to switching to our own server, but I had zero clue as to what or how to fix it.