In short: this is a code issue, not a hosting issue, so there is not a lot we can do to help you with this. Please make sure you installed your website correctly.
If you’re sure that it is installed correctly and you’re using off-the-shelf software, please contact the developers of the software about this. If you’ve written this software yourself, you’ll need to fix your code yourself.
For the technical details: the error says that a PHP constant CURRENT_VERSION was referenced in the code, but this constant does not exist. That’s not a constant that’s part of PHP itself, so it should have been defined in the website code, but it isn’t. That either means that the code responsible for this is not being loaded or is not being executed.