[rt-users] Update to RT 4.2.1 -> JSON error after login

[Dr. Dirk Pape]

Hello,

I updated my RT test server to 4.2.1 (from 4.2.0) and after
 - stopping apache
 - clearing caches
 - starting apache

I see the login page, but when I login RT signals an internal error.

In the Log:
> [13817] [Fri Nov 22 08:17:15 2013] [error]: encountered object '1', but neither allow_blessed, convert_blessed nor allow_tags settings are enabled (or TO_JSON/FREEZE method missing) at /usr/local/share/perl/5.10.1/JSON.pm line 154.
> 
> Stack:
>   [/usr/local/share/perl/5.10.1/JSON.pm:154]
>   [/var/www/vhosts/server.drdpc.de/rt-test/sbin/../lib/RT/Interface/Web.pm:196]
>   [/var/www/vhosts/server.drdpc.de/rt-test/sbin/../lib/RT/Interface/Web.pm:3890]
>   [/var/www/vhosts/server.drdpc.de/rt-test/share/html/Elements/JavascriptConfig:79]
>   [/var/www/vhosts/server.drdpc.de/rt-test/share/html/Elements/HeaderJavascript:48]
>   [/var/www/vhosts/server.drdpc.de/rt-test/share/html/Elements/Header:79]
>   [/var/www/vhosts/server.drdpc.de/rt-test/share/html/index.html:4]
>   [/var/www/vhosts/server.drdpc.de/rt-test/sbin/../lib/RT/Interface/Web.pm:680]
>   [/var/www/vhosts/server.drdpc.de/rt-test/sbin/../lib/RT/Interface/Web.pm:368]
>   [/var/www/vhosts/server.drdpc.de/rt-test/share/html/autohandler:53] (/var/www/vhosts/server.drdpc.de/rt-test/sbin/../lib/RT/Interface/Web/Handler.pm:211)


apache-conf is mod_perl2 with a preloaded rt-server parent process for the virtual host
Extensions installed and loaded: 

> Set( @Plugins,(qw(RT::Extension::MergeUsers RT::Extension::ResetPassword)) );
> Set( @MailPlugins, 'Auth::MailFrom', 'Auth::Crypt' );


I already tried:
 - using another browser (emptying and disabling caches in browser)
 - update Perl-module JSON to latest version
 - update Mason to latest version

My produtive RT (4.2.0) is still running even after apache restart with the same perl instance.
I dare not cleaning caches though. 

Help is really appreciated.

Dirk