I was setting up a new site and installing all my plugins. When I tried to install GP Premium, I got an error message the the zip file was not a zip file. Other plugins could still be installed with no problems. I disabled all the active plugins and GP Premium installed just fine. Here is a list of the other plugins I had installed. One of them must be the conflict.
Upload Larger Plugins
I did that already. No help. I am suspecting the “Upload Larger Plugin” could be the problem. I usually load that near the end, right before I load UpdraftPlus. UpdraftPlus needs it because it is a 4+mb plugin and my upload limit is set at 2mb. I will confirm that the ULP plugin is the problem with the next site I create. I’ll post a follow up.