Referenced resource is not a DITA resource

[liyan]

I append a child and add a reference to a topic, it comes back as an error that it is not a dita resource or the file is not found. Why is this happening.
Please see the following picture:


Please help me solve the issue. Thank you!!!

[Radu]

Hi,
And if you open that specific topic in Oxygen, do you get validation errors reported on it?
Regards,
Radu

[liyan]

Hi Radu, yes. I guess something is wrong with the topic itself.

[Radu]

Hi,

I also assume this, maybe you can switch the topic to the Text editing mode and paste in a codeblock in a reply part of the topic, at least the top part which contains the DOCTYPE declaration.

Regards,
Radu