_pickle.UnpicklingError: could not find MARK

This error occurs when Python's pickle module is unable to unpickle the object because it cannot find the MARK object. The MARK object is a special object created by the pickle module during the serialization process to mark the beginning of a new object.

There are several reasons why this error could occur:

1. The data being unpickled is corrupt or incomplete.
2. The data was pickled by a different version of Python or with different pickle settings.
3. The data was tampered with or modified after being pickled.

To resolve this error, you should try the following:

1. Check that the data being unpickled is not corrupt or incomplete.
2. Make sure that the data was pickled with the same version of Python and pickle settings that you are using to unpickle it.
3. If you suspect that the data has been tampered with or modified, try to obtain a fresh copy of the data.

If none of these solutions work, you may need to consider using a different serialization format or implementing a custom serialization solution.