Couple of problems here: check your ACE driver - if you are trying to use an office 2010 or higher DB, you need ACE OLEDB V14, not V12.
Second, "DataSource" in your connection string should be "Data Source", and the backslashes in your string should be single, not double. Double backslash is only needed when '\' is an escape character for your string such as in C# - not in config files.
You should be able to create a "working" connection string using a UDL file:
Simple SQL Connection String Creation[
^] - I know it works for SQL Server, but haven;t tried it for MDB files via ACE (and I don't have ACE installed on this machine).