We noticed we were no longer getting Gravity forms email notifications (a separate but related issue probably) and I went to the hosting support page and saw that the night before they had done some upgrades to the Parallels Operating System and upgraded from php 5.2 to 5.3, so I started investigating that issue. When I went to go to network admin (I'm running a WordPress network) to disable plugins to test, I was getting 500 internal server error. Then I realised that the front end of the site that's the main site of the network was also getting the error: http://e-business.ie. Checking my stats the site has been down since the hosting upgrade completed. Of the 7 sites in the network, I am getting this 500 error for 3 of them. The one thing they have in common is that they are registered under a different account on the hosting control panel. Though one of them I haven't even mapped yet, so shouldn't be a problem. I can't access the admins of these to see if there may be a common plugin, etc.
I have the hosting company checking it out, but I'm afraid that they'll just come back and say that it's a WordPress issue and I have to deal with it. I've seen other posts re issues with upgrades to the php but none like this exactly. As it's only those domains I'm wondering if it's an issue with Parallels. I can't access Domain Mapping to make sure that it isn't anything there.