I've found that my application does not find my mdb file anymore! I have used a open file dialog box to select the mdb file that I want my app to use and add it to my connectstring via a variable, but although the variable has the correct path to the db, when I'm trying to open my connection to the oledb, it comes back saying that the database cannot be found.
I remembered that I had the "Error List" window minimized, so when I opened it, it was saying that it couldn't find the database - then I realized that somehow, in my Solution Explorer window, the path to my db (that I was no longer using!) was pointing to a 'file' that was where my db was - it was looking there all the time. So I removed the db reference from within my Soluton Explorer and was then able to compile my app successfully.
Because it was looking for a file in my Solution Explorer, none of the changes I made to the db location in code made any difference, but once that reference was removed, I was then able to debug my code as I should.