diff --git a/rhodecode/lib/markup_renderer.py b/rhodecode/lib/markup_renderer.py
--- a/rhodecode/lib/markup_renderer.py
+++ b/rhodecode/lib/markup_renderer.py
@@ -538,20 +538,20 @@ class MarkupRenderer(object):
             body = '\n'.join([header, css, js, body])
             return body, resources
 
-            captured_errors = {}
-            # TODO: In the event of a newer jupyter notebook version, consider increasing the as_version parameter
-            notebook = nbformat.reads(source, as_version=4, capture_validation_error=captured_errors)
-            try:
-                (body, resources) = as_html(notebook)
-            except AttributeError:
-                error_messages = '<br>'.join(str(error) for error in captured_errors.values())
-                body = f"""
-                        <div style="text-align: center;">
-                            <h3>Invalid Notebook!</h3>
-                            <p>{error_messages}</p>
-                        </div>
-                    """
-            return body
+        captured_errors = {}
+        # TODO: In the event of a newer jupyter notebook version, consider increasing the as_version parameter
+        notebook = nbformat.reads(source, as_version=4, capture_validation_error=captured_errors)
+        if captured_errors:
+            error_messages = '<br>'.join(str(error) for error in captured_errors.values())
+            body = f"""
+                    <div style="text-align: center;">
+                        <h3>Invalid Notebook!</h3>
+                        <p>{error_messages}</p>
+                    </div>
+                """
+        else:
+            body, _ = as_html(notebook)
+        return body
 
 
 class RstTemplateRenderer(object):