Hi James, Dom, We've just reproduced the issue here, and it looks like it is indeed an issue with JSON::XS (pulled in by default as a recommend of libjson-perl) with mod_perl. This is with stock configuration and no customization to RT.
To reproduce, install the following: apache2, request-tracker4, rt4-apache2, libapache2-mod-perl2 then in /etc/apache2/sites-enabled/000-default.conf: Include /etc/request-tracker4/apache2-modperl2.conf Ensure that the perl and actions modules are enabled, start up apache, attempt to log in, get the error and see in the log: #---8<----------------------------------------------------------------- [20807] [Tue Apr 25 14:55:15 2017] [info]: Successful login for root from 192.168.100.1 (/usr/share/request-tracker4/lib/RT/Interface/Web.pm:831) [20807] [Tue Apr 25 14:55:15 2017] [error]: encountered object '1', but neither allow_blessed, convert_blessed nor allow_tags settings are enabled (or TO_JSON/FREEZE method missing) at /usr/share/perl5/JSON.pm line 154. Stack: [/usr/share/perl5/JSON.pm:154] [/usr/share/request-tracker4/lib/RT/Interface/Web.pm:193] [/usr/share/request-tracker4/lib/RT/Interface/Web.pm:4396] [/usr/share/request-tracker4/html/Elements/JavascriptConfig:87] [/usr/share/request-tracker4/html/Elements/Header:64] [/usr/share/request-tracker4/html/index.html:4] [/usr/share/request-tracker4/lib/RT/Interface/Web.pm:696] [/usr/share/request-tracker4/lib/RT/Interface/Web.pm:375] [/usr/share/request-tracker4/html/autohandler:53] (/usr/share/request-tracker4/lib/RT/Interface/Web/Handler.pm:209) #---8<----------------------------------------------------------------- (I haven't tried with fcgi/fastcgi, because I couldn't trivially get the appropriate apache config sorted; hopefully, however, this gives you enough to go on.) Hope this helps, Michael -- Michael Howe, Infrastructure and Hosting Team Systems Development and Support IT Services, University of Oxford