Unable to access shared files

Hi Sebastian, 

Welcome to the Box Community, I'm happy to help!

This error message can happen when a user's Box email address is different from the email address the invitation was sent to.

Example:

1. A user's box account email address is: janedoe@domain.com.
2. Their email inbox is signed into jdoe@domain.com.
3. They are invited to a folder using the email janedoe@domain.com and accept the invite from their inbox.
4. They will receive the error same as the one you shared in their Box account

For more details about this error and tips on how to resolve this issue, please take a look at this article: https://support.box.com/hc/en-us/articles/360043693194-Unable-to-Access-Content-User-Signed-into-Wrong-Account 

Thanks for reaching out and  stay safe!

Regards,