One of the very first things it should then be trying to do is create the directory. Did this succeed? I would also be leery of this thing trying to chmod it to 777, which is a no-no on Lunarpages (suPHP is running). It will be able to chmod, but then any further actions in that directory are dead meat (500 error). It's possible that LP has not tried every Softaculous package installation.
If you can't get anywhere, think about getting the Zenbership install package from their site (I presume it's available) and doing a manual install. At least, you can look inside their install script and see what it's trying to do. I don't trust "one button" installers, be they Softaculous or any other brand. cURL usage can also be a problem, but if Softaculous always uses it, then presumably it's properly configured for LP. Any sign of where it's trying to remotely run on, or what it's trying to do with cURL?