I've been working on this for several sessions with the person having the issue

we found out that it was due to AOL Tech Fortress (a malware blocker).

AOL Tech Fortress for AOL Members: Help Stop Computer Threats

I guess it was flagging the install as malware attemp.t

Going to settings remove program, and picking uninstall AOL Fortress  allowed the

horizon client to install with no issues.

I've never seen this before... was interesting, but glad its solved, version 5.10 is now working