I've created the one HTML content whose type is 'template' and now I'm trying to call that content using the AMPscrip function '%%=ContentBlockbyId("384201")=%%' in blank email template but it gives the error which in the below screenshot,
As per your question, you have created an HTML paste template whose ID is 384201. And you are trying to call this template in your email(and you are using blank template in this email, correct?).
You are getting this error because you need to create a content block(you can create HTML content block) instead of a template and then call that content block using ContentBlockbyID function in your email. You cannot call a template inside an email by using ContentBlockbyID function.