All links work for me in a clean install. I even have vanilla installed in a special directory not called "vanilla" and it still works :-) I didn't upgrade though.
I encountered this as well. In my case it was the "Vanilla Statistics" plugin that was causing the problem. If you have that enabled, try disabling it. If that is not the source you should change to debug mode to get a better idea where it might be happening. You do that by adding / changing the default in your conf/config.php settings file to the following:
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What to do if I get a Bonk Error?
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Deploying a new Forum and adding a Theme
I encountered this as well. In my case it was the "Vanilla Statistics" plugin that was causing the problem. If you have that enabled, try disabling it. If that is not the source you should change to debug mode to get a better idea where it might be happening. You do that by adding / changing the default in your conf/config.php settings file to the following:
$Configuration['Garden']['Errors']['MasterView'] = 'deverror.master.php';
Cheers