You've given us some info, General, but maybe not enough.  Where did you install your Poser content?  W7, as Vista, does have issues with apps installed into Program Files folder.  If you search the forum, there are countless posts about this subject.  It may explain the intermittent library function.  If this is the case, my suggestion is to either shutdown UAC completely or move your Poser installation into its own folder on your core drive.