What is a schema error? And how can I fix it?

Question

So... I've gotten this error https://imgur.com/yOSngsw on opening my old project to try and get some screen captures for a showreel. 

I've done a bit of research and it's pointing to me editing the WWU XML file via a text editor but I'm way out of my depth. Is there an easy fix for this? 

I haven't merged the file or used version control, and the project was opening fine last week. So I'm unsure as to why this is happening. 

Any help would be greatly appreciated! 

Comments

Can anyone help me?? I'm dying here. I cant even open my project?

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I have update the wwise project to the lastest version but still not working. Any advice?