It's looking for Poser.exe, and if you have Poser Pro it's named PoserPro.exe which is why the DAZ installer can't find it.

Easiest way around it is to choose "DAZ Studio" when you install the content, that way it won't look for Poser.exe and will install all the files (including DAZ Studio materials)

(And, for what it's worth ... zip files are so much easier. LOL)