They do not have the same meaning: digitalisation (digitalization) is the process of making something digital, for example scanning a paper document into a pdf is digitalisation. Digitisation is turning something into digits, or numbers. While digital material is usually an expression of binary numbers, digitisation usually refers to something more numerical in nature, for example taking a large sample of things and counting them so that you have a discrete value to work with at the end. For example, if you have done a survey and want to analyse the data, you would have to digitise it first.

In my opinion, both words are correct. 1. Digitalization or digitalisation: the integration of digital technologies into everyday life by the digitization of everything that can be digitized. -"to digitize." 2.Digitization or digitisation: the process of converting information into a digital format. This term is often used when diverse forms of information such as objects, text, sound, images or audio are converted into an electronic digital code that can be read by computers or other electronic devices.

I am using OpenOffice today and it's accepting both forms as well as the UK spellings with an -s instead of a -z. I've only seen "digitalisation" which seems more correct to me because it is the process for making something "digital" not "digit".