Try re-installing the SambaPOS. If this does not work, then remove .Net Framework and SambaPOS and start a clean install, during the install it should prompt you to download and install .NET framework.
From memory that error means that .NET has corruptions or another program has changed some settings within .NET that relates to using ODBC connections which is used to connect to the database.
I think I removed all .NET and all .NET directories from the system and reinstalled all the .NET versions I had removed.