Sometimes syntax errors are detected

[sam.s.kong]

Hi!

When I create or modify an asp file, obvious systax errors are not
detected.
For example:

Sub MySub
Response.Write "Hello"
End

It should end with "End Sub".
But the server displays an error message like "Cannot display page".
And I copy and delete all content in the source file, save it as an
empty file, reload the page and the page displays an empty page.
Now I paste the source into the file, save it, reload it, and the page
displays the correct systax error with line number.

Why can't the error be detected in the first place?

Sam