diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a140f6043..6b63ba96e4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,8 @@
 - Update depedencies by [@pngwn](https://github.com/pngwn) in [PR 4643](https://github.com/gradio-app/gradio/pull/4643)
 - The theme builder now launches successfully, and the API docs are cleaned up. By [@abidlabs](https://github.com/aliabid94) in [PR 4683](https://github.com/gradio-app/gradio/pull/4683)
 - Remove `cleared_value` from some components as its no longer used internally by [@freddyaboulton](https://github.com/freddyaboulton) in [PR 4685](https://github.com/gradio-app/gradio/pull/4685)
+- Better errors when you define two Blocks and reference components in one Blocks from the events in the other Blocks [@abidlabs](https://github.com/aliabid94) in [PR 4738](https://github.com/gradio-app/gradio/pull/4738).
+
 
 ## Breaking Changes:
 
diff --git a/gradio/analytics.py b/gradio/analytics.py
index c4b710aa26..6724619ae1 100644
--- a/gradio/analytics.py
+++ b/gradio/analytics.py
@@ -120,10 +120,10 @@ def launched_analytics(blocks: gradio.Blocks, data: dict[str, Any]) -> None:
             if y in blocks.blocks
         ]
         inputs_telemetry = inputs_telemetry + [
-            str(blocks.blocks[y]) for y in x["inputs"]
+            str(blocks.blocks[y]) for y in x["inputs"] if y in blocks.blocks
         ]
         outputs_telemetry = outputs_telemetry + [
-            str(blocks.blocks[y]) for y in x["outputs"]
+            str(blocks.blocks[y]) for y in x["outputs"] if y in blocks.blocks
         ]
     additional_data = {
         "version": GRADIO_VERSION,
diff --git a/gradio/blocks.py b/gradio/blocks.py
index bf6bc1f9de..b3369f8356 100644
--- a/gradio/blocks.py
+++ b/gradio/blocks.py
@@ -36,7 +36,11 @@ from gradio import (
 )
 from gradio.context import Context
 from gradio.deprecation import check_deprecated_parameters, warn_deprecation
-from gradio.exceptions import DuplicateBlockError, InvalidApiNameError
+from gradio.exceptions import (
+    DuplicateBlockError,
+    InvalidApiNameError,
+    InvalidBlockError,
+)
 from gradio.helpers import EventData, create_tracker, skip, special_args
 from gradio.themes import Default as DefaultTheme
 from gradio.themes import ThemeClass as Theme
@@ -1116,7 +1120,12 @@ class Blocks(BlockContext):
         processed_input = []
 
         for i, input_id in enumerate(dependency["inputs"]):
-            block = self.blocks[input_id]
+            try:
+                block = self.blocks[input_id]
+            except KeyError as e:
+                raise InvalidBlockError(
+                    f"Input component with id {input_id} used in {dependency['trigger']}() event is not defined in this gr.Blocks context. You are allowed to nest gr.Blocks contexts, but there must be a gr.Blocks context that contains all components and events."
+                ) from e
             assert isinstance(
                 block, components.IOComponent
             ), f"{block.__class__} Component with id {input_id} not a valid input component."
@@ -1130,7 +1139,12 @@ class Blocks(BlockContext):
         predictions = []
 
         for o, output_id in enumerate(dependency["outputs"]):
-            block = self.blocks[output_id]
+            try:
+                block = self.blocks[output_id]
+            except KeyError as e:
+                raise InvalidBlockError(
+                    f"Output component with id {output_id} used in {dependency['trigger']}() event not found in this gr.Blocks context. You are allowed to nest gr.Blocks contexts, but there must be a gr.Blocks context that contains all components and events."
+                ) from e
             assert isinstance(
                 block, components.IOComponent
             ), f"{block.__class__} Component with id {output_id} not a valid output component."
@@ -1191,7 +1205,12 @@ Received inputs:
         if block_fn.preprocess:
             processed_input = []
             for i, input_id in enumerate(dependency["inputs"]):
-                block = self.blocks[input_id]
+                try:
+                    block = self.blocks[input_id]
+                except KeyError as e:
+                    raise InvalidBlockError(
+                        f"Input component with id {input_id} used in {dependency['trigger']}() event not found in this gr.Blocks context. You are allowed to nest gr.Blocks contexts, but there must be a gr.Blocks context that contains all components and events."
+                    ) from e
                 assert isinstance(
                     block, components.Component
                 ), f"{block.__class__} Component with id {input_id} not a valid input component."
@@ -1269,7 +1288,14 @@ Received outputs:
                     "Number of output components does not match number "
                     f"of values returned from from function {block_fn.name}"
                 ) from err
-            block = self.blocks[output_id]
+
+            try:
+                block = self.blocks[output_id]
+            except KeyError as e:
+                raise InvalidBlockError(
+                    f"Output component with id {output_id} used in {dependency['trigger']}() event not found in this gr.Blocks context. You are allowed to nest gr.Blocks contexts, but there must be a gr.Blocks context that contains all components and events."
+                ) from e
+
             if getattr(block, "stateful", False):
                 if not utils.is_update(predictions[i]):
                     state[output_id] = predictions[i]
diff --git a/gradio/exceptions.py b/gradio/exceptions.py
index 3dcf67e76e..903e505e3c 100644
--- a/gradio/exceptions.py
+++ b/gradio/exceptions.py
@@ -23,6 +23,12 @@ class ServerFailedToStartError(Exception):
     pass
 
 
+class InvalidBlockError(ValueError):
+    """Raised when an event in a Blocks contains a reference to a Block that is not in the original Blocks"""
+
+    pass
+
+
 InvalidApiName = InvalidApiNameError  # backwards compatibility
 
 
diff --git a/test/test_blocks.py b/test/test_blocks.py
index 3490eb3d99..83b52b00dc 100644
--- a/test/test_blocks.py
+++ b/test/test_blocks.py
@@ -212,10 +212,25 @@ class TestBlocksMethods:
     @mock.patch("requests.post")
     def test_initiated_analytics(self, mock_post, monkeypatch):
         monkeypatch.setenv("GRADIO_ANALYTICS_ENABLED", "True")
-        with gr.Blocks(analytics_enabled=True):
+        with gr.Blocks():
             pass
         mock_post.assert_called_once()
 
+    @mock.patch("requests.post")
+    def test_launch_analytics_does_not_error_with_invalid_blocks(
+        self, mock_post, monkeypatch
+    ):
+        monkeypatch.setenv("GRADIO_ANALYTICS_ENABLED", "True")
+        with gr.Blocks():
+            t1 = gr.Textbox()
+
+        with gr.Blocks() as demo:
+            t2 = gr.Textbox()
+            t2.change(lambda x: x, t2, t1)
+
+        demo.launch(prevent_thread_lock=True)
+        mock_post.assert_called()
+
     def test_show_error(self):
         with gr.Blocks() as demo:
             pass