I also experienced this from the last snapshots, from July 18 - 31. All I have to do is uninstall and reinstall. Although my chance of success was very minimal, but it worked later on. I think it has something to do with the packages. I also experienced this perl error with ntop and squid.
Aside from that, this is what I experienced in the last few days: http://forum.pfsense.org/index.php/topic,39420.0.html
There were also times that the installation was a success, but I cannot find the menu in the gui. So when I remove the package or do a reinstall, the installation process got to a halt or hang.