Azure AI Agent returns "ValueError: Toolset is not available in the client." when using function tools across modules

I'm working with Azure AI Agents and trying to use custom functions within an agent. I've defined several user-defined functions and wrapped them using FunctionTool, then added them to a ToolSet. Here's how I've structured my code:

    {
        func1, 
        func2, 
        func3, 
        func4, 
        func5
    })

   func_fetching_toolset = ToolSet() 
   func_fetching_toolset.add(functions_tool)

    agent = project_client.agents.create_agent(
        model=os.environ.get("AZURE_AOAI_CHAT_MODEL_NAME_DEPLOYMENT_ID"),
        name="func-fetching-agent", 
        instructions="""        
                You are an advanced assistant capable of calling user-defined functions when necessary. 
            """,
        toolset=func_fetching_toolset,
    )

When I create a thread and run it, I encounter the following error:

ValueError: Toolset is not available in the client.

Observations:

• If I move all the code into a single file (i.e., combine tools.py and main.py), the error does not occur, and everything works as expected.
• This suggests the issue arises when the ToolSet is defined in one module and used in another.

My Question:

• Why am I getting the ValueError: Toolset is not available in the client. error when the agent is created in a different file from where the ToolSet is defined?
• How can I properly use a ToolSet defined in one module (tools.py) within an agent created in another module (main.py)?

What I've Tried:

• Ensured that func_fetching_toolset is correctly imported into main.py.
• Checked that all dependencies and environment variables are correctly set.
• Verified that the ToolSet and FunctionTool are correctly constructed.

I too was having this very issue and the thing that solved it for me was passing the toolset while creating the run.

project_client.agents.create_and_process_run(thread_id=thread.id, assistant_id=agent.id, toolset=toolset)