Can't Do A Successful Make With Prima 1.23

Hello all! This is my first time emailing the list, and I'm eager to be
joining the fray.

Unfortunately I'm still a little wet behind the ears when it comes to linux
or installing perl toolkits. I am trying to install Prima 1.23 on my linux
distribution with gtk2 from a tar file I received on your website.
Makefile.PL works just fine, however whenever I try any of the makes I
receive an error:

In file included from Icon.c:31:
include/img_conv.h:35:16: error io.h: No such file or directory
make: *** [Icon.o] Error 1

I was not able to find enough information anywhere to try and remedy this
problem. Any light you guys could shine on this would be great. Thanks in
advance!

-- 
Ian Campbell
Staff Programmer
Mechanized Propulsion Systems, Inc.