My other templates open fine from the EE backend, but when I try to open my layout template I get the following message:
Call to a member function getId() on null in [path]/ee/EllisLab/ExpressionEngine/Controller/Design/Template.php
I can see and open the template in my ftp program, but can't open it from inside of EE.
I'm running version 5.3.0
<h1>Hello World</h1>) and seeing if issue goes away? If it works, suggests the issue is in the content of your template, if it doesn't suggests an EE config / setup issue. Either way, to get more / better help usually helpful to include details of what version of EE you are having problems with in your question. HTH.