Why do some pages give a 500 error after transferring the site to another hosting?

Question

PHP

Good afternoon everyone! Prompt, please, in what direction to dig. After transferring the site to a new hosting, some pages with categories are no longer displayed. At first, the whole site was not displayed at all, the support service sent a comment:
[error] [client 89.109.194.144] malformed header from script. Bad header=X-Content-Type-Options nosniff: index.php
We closed the line
//header("X-Content-Type-Options nosniff");
Everything worked, except for a few category pages.
PS The engine is self-written.

Answer 1

Wangyu that the colon between the header name and its value was forgotten.