A fix
After reading through numerous posts in various subforums about problems with this latest build, I came across a solution. The problem was that Parallels was unable to install Parallels Tools, because of an autoplay setting in Vista. Seems that Vista sees the Parallels Tools installation program as a CD-ROM, and you have to have Vista set up to autorun/install program CDs. Went to Control Panel, changed that setting, and was able to install Parallels Tools ... which then fixed the problem with Coherence.
No idea why Vista suddenly had a problem with this build, but that's what fixed it.