Since there was enough interest in my two-year-old program, ErrorGen, I've created a Perl/Tk module that does basically what ErrorGen does.
Here's a screenshot:
It's only a module so far that can be included in other Perl/Tk applications. But it's one very large step closer to me creating a simplified tool to spawn error boxes which could be provoked from batch files or scripts. It will probably have a syntax similar to the GNOME program, Zenity.
CPAN takes a few hours to index module updates but the new module will be available at Tk::StyleDialog on CPAN.org.
UPDATE: I've thrown together a quick program called ZenMsg (a name derived from GNOME's Zenity, but since my program only does dialog boxes, it's called ZenMsg).
I've added it as a new tab to the ErrorGen page. Let me know if it can be improved. I had to use ActiveState PerlApp to compile it because PAR::Packer (which I usually prefer to use) was giving me trouble and I didn't have the time or motivation to setup a clean new compiling environment for it. PerlApp may be a bit too limiting.