Snapshot Pro install fail

I am trying to install Snapshot Pro to test it. In the WPMU Dashboard when I find Snapshot Pro and click Install I get a popup message that the install failed. The message says that the most likely reason is that the permissions on wp-content are not correct. This is nonsense as I have installed many plugins on this site and have had no such issues. I have plenty of disk space. I also have several WPMU plugins installed and working on the site.

Please advise.