I'm not familiar with RoR, but there are lots of things that can trigger a 500 error. If you brought over .htaccess (and any equivalent of php.ini files) from your old host, there could be commands in it that are not valid on your new server, such as Mod Security settings. Some hosts still permit "world writable" permissions (e.g., 666 and 777) -- those are forbidden here. With PHP, an empty or blank line at the beginning or end is not allowed -- check for that, maybe RoR has the same restriction. You've checked that your files came over properly formatted (i.e., end-of-line is correct)? There's lots of PHP-specific stuff (phpvalue and phpflag, for instance) that may or not be applicable to your case (I don't know what the RoR equivalents are).