Hi Kristian,
The “Error” you are mentioning is not an Error, it is a Notice. These are the lowest form of php server responses and will not stop a page from loading or showing up. This is merely a notice that a variable was used before it was defined (and php makes up for that on its own).
My guess is that something else is happening, like the server is running out of memory during an execution or something else is going on and this just happens to be the only notice you are receiving.
For the hosting company to immediately say it is the plugin is not really the correct response, as the plugin is used by hundreds of thousands of sites and you are having a problem that no one else is having, makes it seem like it is either a programming error someplace (in another plugin or theme file), or like I mentioned, the server is running out of resources before the site finishes loading a page. This is very common when adding a new plugin because if the site is JUST making it with the amount of memory it was using, adding something new to the process could push it over the top.
Check your memory usage for the site. Many hosts like to try to set them default limits to the lowest they can be to run – and the more things you run, the more posts and data you process, the more you need. anther thing that can affect memory usage is the version of PHP you are running. I think the average WordPress install needs about 30-40mb of ram for itself and then anything else can add to that.
That would be my suggestion for where to start looking for the issue.
Additionally, if, by chance, you created a looping redirect by redirecting one page to another that loops back to the original one, you may need to clear the browser cache or enter the site via an incognito or private browser tab and go to the admin first and check things out. Browsers will cache 301 redirects and that may be the only was for you to access it until it clears or lets go of the cache. Usually when this happens, everyone else can see it fine, just not you as your browser is the one storing the cache.
Regards,
Don
