I just upgraded to 4.0.3 and have started to have problems after adding a book manually. All my books are old so there is no ISBN. I enter all the info go to "add" or "add & new" and all I get is a spinning ball. All the work is for nothing.
That was a bug I added in that version. It is fixed now and you can download the program again to get the fix right away. The version is still 4.0.4 and it will official when the version number changes next.