Hi again Jimena,
Is that the whole of the EAD XML output when you try to export the description?
If so, then the original error message makes sense to me - this EAD file is incomplete. There are several open elements ( such as the <archdesc> element, and the opening <ead> element) that do not have corresponding closing elements in the file currently. It's possible this would trigger a message like the one you reported: "Error reported by XML parser: Premature end of file."
As for why the EAD is being truncated:
I would recommend that you revisit the last suggestion from my first email, and check the contents of your description. Did you copy and paste this content from another source, such as a Microsoft Word document for example? If yes, then it may contain non UTF-8 characters that break the XML rendering.
For example, in the <bioghist> element I can see some of the non UTF-8 "curly" quotation marks:
...ordenó y devolvió al Estado boliviano; 3) Historiográfica, cuya cumbre es “Últimos días coloniales en el alto Perú”; 4) Crítica, en su juventud se dedicó a analizar a los poetas románticos. Su aporte al conocimiento del país ha sido trascendental sin que hasta el momento de su muerte nadie pueda igualarlo.</p>
If you need to cut and paste content from another source, I recommend finding a way to ensure it is UTF-8 first. For example, you'll find many online guides on how to ensure that Word documents are saved in UTF-8; here are two resources I found quickly:
There are also online encoding converters where you can paste content.
Don't forget the other suggestions in the first email as well - check for < > characters or HTML elements in the description and remove them if possible, since they can break the conversion to XML.
I hope this helps to resolve the issue! Let us know how it goes.