I probably should have posted to the Installation forum. Judging from the blog post that is referenced, it's a wider issue than just Civil 3D. Since this is a known type of install issue, it would be nice to include a heads-up in the readme file. Some of us read those... Guess it was easy enough to google once I figured out it was workstation specific. We resolved it by moving all the zlib.dll files to the Recycle Bin (there were many due to various programs, including Trimble Business Center), installed C3D then restored them.
Lisa
Lisa Pohlmeyer
Williamson County Dept. of Infrastructure<>
direct: 512-943-3364
main: 512-943-3330