Hi Tammy McCarron 
The first step would certainly be to make a backup copy of the *original* SDLXLIFF file - the way it was *before* you started to modify it with a text editor. Keep this backup, never modify it until your problem is solved. You might need a couple of tries, and this backup copy is where you can get fresh copies from for the next attempt. This procedure should be standard whenever there is a corrupt file.
As for the specific problem, I would not know how to remote-diagnose, it's a bit too complex. (For me, at least.)

Does this help: stackoverflow.com/.../hexadecimal-value-0x00-is-a-invalid-character

[Edit] Or this: https://gateway.rws.com/csm?id=kb_article_view&sysparm_article=KB0034155

All the best.
Daniel

Hello Tammy McCarron 

Where possible, please always post the full error stack in community as the more information we have the easier it is to offer a solution.

Based on the information you have provided, maybe the following article will help

https://gateway.rws.com/csm?id=kb_article_view&sysparm_article=KB0034155