I ran into a situation today after formatting my computer where I opened a VS project on a mapped network drive and received the error about the project location not being trusted.
After lots of researching I found an article that helped me a little bit: check it out here.
Like I said, it helped me a little bit. I had to go further and experiment with different command line calls because what was in the link above did not work for me. I ended up using two commands before I finally got the warning message to go away. Here are those lines:
caspol -rg 1.3.1
caspol -m -ag 1.3 -allcode FullTrust
The first line removes the policy at 1.3.1. Then I add a new policy in that gives the All Code group full trust. 1.3 is the Internet zone. I tried adding the same thing to the Intranet zone but that did not work for me.
Hope this helps for anyone else running into this problem.