Same problem here… I have e new installation of RT4.4.2 under debian, then installed RT-IR-4.0.0 and the error you mention appears… tried RT-IR-4.0.1rc1 too
here is the output of make intidb:
Couldn't finish 'insert' step.
ERROR: Couldn't load data from 'etc/initialdata':
ERROR:Can't locate etc/initialdata in @INC (@INC contains: /opt/rt4/sbin/../local/lib /opt/rt4/local/plugins/RT-IR/lib /opt/rt4/sbin/../lib lib /opt/rt4/local/lib /opt/rt4/lib /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 /usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /opt/rt4/sbin/../lib/RT/Handle.pm line 917.
Do you have the correct initialdata handler in RT_Config for this type of file?
...returned with error: 65280
Makefile:1018: recipe for target 'initdb' failed
make: *** [initdb] Error 2