Just to let you know I've solved the problem (with a spot of help!). Final solution was to use the full database name of "YOUR-56C1234567\SQLEXPRESS". I then...
I'm getting exactly the same problem and I don't know how to solve it. I've tried a variety of different styles for the database e.g. "YOUR-56C1234567" and "YOUR-56C1234567\SQLEXPRESS"....