LangChain-SQLDatabaseChain: Type error for SQLDatabase

I use a code to create a SQLDatabaseChain with LangChain that once worked just fine. However, it does not work anymore, which is very strange. Here is the part that's causing the error:

llm = ...
memory = ...
db = SQLDatabase.from_uri("sqlite:///Test.db")
print(type(db)) --> <class 'langchain.utilities.sql_database.SQLDatabase'>
print(db) --> <langchain.utilities.sql_database.SQLDatabase object at 0x0000015965D4F7D0>

sql_chain = SQLDatabaseChain.from_llm(
        llm=llm,
        db=db,
        verbose=True,
        memory=memory,
        use_query_checker=True,
        top_k=20,)
...
result = sql_chain({"query": question}, return_only_outputs=False)
...

This is the error I get:

ValidationError                           Traceback (most recent call last)
File c:\Users\...\SQLChain-Test_01.py:1
----> 1 sql_chain = SQLDatabaseChain.from_llm(
      2     llm=llm,
      3     db=db,
      4     verbose=True,
      5     memory=memory,
      6     use_query_checker=True,
      7     top_k=20,)

File c:\Users\...\Lib\site-packages\langchain_experimental\sql\base.py:228, in SQLDatabaseChain.from_llm(cls, llm, db, prompt, **kwargs)
    226 prompt = prompt or SQL_PROMPTS.get(db.dialect, PROMPT)
    227 llm_chain = LLMChain(llm=llm, prompt=prompt)
--> 228 return cls(llm_chain=llm_chain, database=db, **kwargs)

File c:\Users\...\AppData\Local\anaconda3\envs\...\Lib\site-packages\langchain\load\serializable.py:97, in Serializable.__init__(self, **kwargs)
     96 def __init__(self, **kwargs: Any) -> None:
---> 97     super().__init__(**kwargs)
     98     self._lc_kwargs = kwargs

File c:\Users\...\AppData\Local\anaconda3\envs\...\Lib\site-packages\pydantic\v1\main.py:341, in BaseModel.__init__(__pydantic_self__, **data)
    339 values, fields_set, validation_error = validate_model(__pydantic_self__.__class__, data)
    340 if validation_error:
--> 341     raise validation_error
    342 try:
    343     object_setattr(__pydantic_self__, '__dict__', values)

ValidationError: 1 validation error for SQLDatabaseChain
database
  instance of SQLDatabase expected (type=type_error.arbitrary_type; expected_arbitrary_type=SQLDatabase)

Strangely, when I check the type of my db it seems to be all correct: print(type(db)) --> <class 'langchain.utilities.sql_database.SQLDatabase'> Any ideas what is happening here? Maybe I am overseeing something.

Langchain version = 0.1.6
Langchain experimental version = 0.0.51
Python version = 3.11.5

Many thanks for any help.