RSS Problem, not validating

Hi all

I am having some problems with RSS – they do not work.

https://feedvalidator.org/check.cgi?url=http%3A%2F%2Fvitorm.webhs.org%2Fblog%2Fwp-rss.php

Sorry
This feed does not validate.
*
line 2, column 0: XML parsing error: <unknown>:2:0: xml declaration not at start of external entity

Can anyone help me?

Thank you