When I try to import bank statements with the Period Lock in place, I get the following screen:
Which confused me for a while, since at first I thought there might have been a problem with the import facility. However, after some fiddling about, I realized that I have the period lock on which was the reason preventing the import. But I had to figure that out on my own.
I think providing the user with the reason for not being able to import would save the user and the forum members significant time and effort. This will also make for a more pleasant user experience.