Sometimes you need to install (or transfer) your site on to the new hosting. And it is a rare occurence that the provider can (or wants to) estimate all the requirements for your site application. Especially when your site isn't based on one of the widely known CMS. There are many things to be wary of: are all the required modules installed? Do they all have the correct versions? Is the PHP version correct and is there enough memory or not and so on.
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