Q: Why is IRAF complaining that os.zgtenv: cannot open `/usr/include/iraf.h'?
Most likely, you did not set the imdir variable in your login.cl as instructed.
Do so. Then, in each directory where you have data files exhibiting this problem, type:
imcopy *.imh *.imh
Credit: This answer was provided by Catherine Cress and Toby Rider.