Is this issue reproducible or was this a one-time event? I see this issue was reported twice in the last few years but the customers could not proceed in debugging their issue because it did not occur again.  I would be interested in seeing the PegaRULES log and maybe we could determine why JBoss could not process the request and told IE to authenticate (or did something to make IE think it needed to authenticate).  It would also be important to determine if the issue is IE-only.

With that said, I did see an article on JBoss forum and it happened to coincide with a comment made on one of the prior SRs in regards to Pega on Tomcat with Kerberos and an anomaly with "token which ends up being large".

http://answers.elteacher.info/questions/post/1238155/skip-sso-for-specific-page-java-webapp-jboss-ask-question.html

Here is the Pega PDN article regarding same.

https://community.pega.com/support/support-articles/sso-login-ie11-kerberos-token-exceeds-tomcat-maxheadersize

Note : please check and mask any proprietary data in your screenshot attached (Case names in tabs and/or IPs in pop-up message).

Thanks for the advice!

The popup  window isn't preventing the user from doignwork, it comes up and they can exit it out. I spoke with two users now and its comes up randomly after idle minutes. They are both "testers" and they are getting this error inside our development environment.

I will take a look at the website you provided and get back to you.

Thanks