This is a post meant to be found on Google by people having the same problem, hopefully this will save them some time.
I spent at least 6 hours knocking my head out because of some strange error the Qt OBDC driver was giving me when trying to access an Access Database file .accdb :
Could not find installable ISAM.
What a strange problem! After playing a bit more with ODBC I also got a new error:
Data source name not found and no default driver specified.
And in the end the problem was coming from the file permissions themselves! It appeared that the database was in read-only (don’t ask me why) and as soon as I corrected this, everything want fine again.
A really cryptic error for such a problem.