I get the 500 Server error when I click to connect to Wordpress.com when setting up Jetpack.
A misconfiguration on the server caused a hiccup. Check the server logs, fix the problem, then try again.
Sorry to hear about the problem you are having with the JetPack plugin for Wordpress. Unfortunately, the link you provided only gets me to your login page. So, I can't see what's going on with the Jetpack installation. I've actually been able to install that plugin myself with no problems, so I'm not sure what may be happening with your installation of it. One thing to consider is that if you already have several plugins, then installing Jetpack after may result in issues. You should try disabling all other plugins first, then installing it. If you problems with the currently loaded Jetpack plugin, then try manually disabling it. You can do this by renaming the plugin folder. You need only do this if you are unable to disable the currently installation of your jetpack plugin.
I did also check the error logs and there is nothing there. It's possible that the problem is related to existing plugins- please try to remove/disable those first, then try running the installation once more.
I tried disabling all other plugins and trying again. Didn't help.
I followed the instructions from the forum posting you linked: Didn't help.
Sorry for the continuing problems. It appears that the plugin was conflicting with a setting within the PHP switch options for cPanel on the server. I was able to actually duplicate the problem with a test Wordpress install on your account, but after working with a systems person internally on the issue, we were able to resolve it. Some code was added to the top of your .htaccess file - please do not remove it. If you continue to have the problem, then please let us know immediately. I was able to see it working on my test site once the changes were applied.
Apologies again for the problems - please let us know if you need further assistance.