The Common Library won't load unless these is an open document. Are you running into this issue when a document is open? Are you MAC or Windows? If this does occur with open documents, does the problem occur with just specific files?
It's always with an open document. I'm using a macbook pro. I had this problem with snow leopard and now lion. In CS4 it seemed to happen consistently across all files. This is the first time it's happened since I upgraded to CS5, so I don't know if it'll happen on different files or not.
The problem does not go away when I close and reopen the file, but it will if I quite fireworks and restart it.
I'm on a MBP as well and not had this issue. I've steered clear of Lion for now until I hear better news from Adobe and Apple about issues. While there's not much listed in terms of Lion issues for Fireworks, things seem to be cropping up here and there.
I'll notify the Fireworks Engineers to your issue. Maybe they can help.