It's come to my attention that the original question was a little unclear.
I'm working on a custom-built YouTube plugin for WordPress which has passed all the tests on my local installation, but as soon as I try to run it on a live site, I start seeing fatal errors on the settings page:
The error occurs during a utility function I have to check whether or not the OAuth authentication is valid.
As shown in the screenshot, I fail when trying to call the
Google_Client::getConfig() function, which is allegedly undefined.
I did a
get_class_methods() in both locations. On my test site, that produced 60 methods, one of which was the expected
getConfig(). On the live site, however, I only had 48 methods, and
getConfig() was not one of them.
It seems likely that there is some sort of versioning issue with the way I've included the Google API, but I haven't been able to zero in on it.
The live site site is clearly loading a different version of the
Google_Client class, but I don't know where that could be coming from because the version I've included in the plugin definitely has the methods in question.