P0w3rK!d,
I am pretty sure your particular build is fine (use threads; doesn't gack right?), even though your install or particular attempt at threading might not be. From the install docs:

Perl Environment Variables: if Perl environment variables such as PERLLIB, PERL5LIB or PERL5OPT have been set on your system, you should unset them before installing ActivePerl. Otherwise, these variables may cause incompatible versions of Perl modules to be used during the installation process.

I also took a look at the Release Notes. It indicates that there is a problem with the emulated fork if the extension isn't thread safe.

I examined the diff file from the standard install to what got compiled for ActiveState - IThreads are in there.

Finally - I found this article, with examples, quite interesting by Jenda.

I would recommend supplying the code and asking for more help.

Cheers - L~R