Ugh
From selenium point of view, page load did took too much time and therefore selenium did raise an exception. There are two common solutions to your problem: 1) Make the page load faster 2) Increases the timeout value.
The former is usually a better solution, if the problem happens in your web application. Just find what is the bottleneck and do something to remove the bottleneck.
The later happens by using the selenium API, set_page_load_timeout [1], but unfortunately that API is not exposed as a keyword in Selenium2Library. But there is a issue [2], which explains how to use the selenium API from as a keyword.
Please note that there are many other uncommon reason why the error may happen and those are not explained.