My apologies on resurrecting an old thread–it most closely identifies with the issue I experienced this weekend.
Did you get find anything else on this issue?
I encountered the same error and stack trace after upgrading my Debian box from Wheezy to Jessie (v9). I was faced with the “an internal error occurred, contact the administrator” page after authentication. After much digging I found your post and applied the same patch which enabled authentication to complete. However, I couldn’t use the advanced search at all as I’d receive a similar error relating to JSON and line 154.
I had used the RT make process to update the perl modules which completed successfully, barring this issue. So I had a half functional RT installation.
As a left field thought I suspected the Debian Perl libraries may . Consequently, I explored the version info for the Debian and the compiled modules for JSON and JSON::XS. The compiled versions were 2.9 and 3.03, whilst the Debian libraries are v2.61 and 2.34 respectively.
Removed the two modules I compiled, installed the Debian libraries instead and RT is now fully functional.
Thought I’d add my experience in case anyone else has a similar experience.