With XPages I use the nhttp preview a lot. Today I wrapped up work using one ID and switched to another one. I had made a simple change and was checking on it and it wouldn't load. The error was that it couldn't open a database - both were on my local, and working for months. It turns out that the nhttp preview was the problem. I shut it down and relaunched the clients and it worked.
I wonder if nhttp has a reload command...