I’m in the same boat.
Hosted on Earthlink, checked every damn plug-in/theme related solution and those failed. My .htaccess is blank, permalinks normal, yada yada yada. This is a completely fresh install, new database and everything, done just like every other install I’ve ever done. Only thing that is different is Earthlink and 3.0. I’m guessing Earthlink has some PHP thingy turned off or something. I contacted their support about it, to no avail. Please let me know if you guys find a solution, thanks!
oh yeah, in case any of you are PHP geniuses, here is what earthlink is providing on the server: https://www.maximludwig.com/phpinfo.php