I have the same problem. There has been numerous posts for this issue, and I am a little bit confused of how people can use it.
To my understanding it seems to be by design that you will need to login through pbpbb, as there is one interface required. But I don’t know whether people who can successfully use this plugin have another way of editing their wordpress settings, enter blog entries, work on the css files etc. Because regardless what I did and I redid everything from scratch, followed the instructions, the widgets and all, still the same issue. I am not going to post the details here but if anyone interested this is one of the threads about this problem.
Can someone who is using this plugin successfully tell us how they work on their wordpress settings and blogs, etc? I started to doubt myself that I am looking for the wrong thing!!!