Disregard my last post, as I thought there was only one page to this thread so far.

It is indeed HUGELY coincidental that 99.9% of us are having this problem as it relates to V4.  But as I am tryin to examine all realms of possiblity, wrap your mind around this:

I ran some tests.  I have two .pz3 scenes I set up today containing V4 (I only purchased her today; prior to my purchase I've never seen the .xml parser error).  Here's what I've seen so far:

The first scene I saved appears to open, although the document window is pitch black, even though the scene is well-lit according to the light globe.  The GUI seems to respond when attempting to open up the "content slider" from the right (I don't know what it's really called) or playing with the parameter dials.  But the light globe is frozen; the lights cannot be added, deleted, etc.

The second scene I saved does not load the document window at all.  All the above hold true as well for this particular scene.  Remember, BOTH scenes contain the new V4.

I can stll open old .pz3 scenes without issue.  Additionally, I created a new scene, added some figures, props, etc. and saved it, closed Poser completely, reopened it, and opened the saved .pz3 successfully.  Then, I added V4 to the SAME scene, saved it as a new name, closed Poser, reopened it, and loaded that .pz3 scene.  It opened successfully.  So why just those two apparently corrupted ones?  Well, I attempted to once again open one; same issues.  Then, I went back to open the recently saved one containing V4. Same issue as the first!  The document window was black (my default background color) and the GUI appeared to respond but nothing happened.

Let's go over the facts:

1.  Most of us have been having this issue since the install of V4 (the bundle)
2.  Been happening since Friday frequently enough to infer something has just recently broke
3.  I believe the majority of us have preordered Poser 7 (giving clout to the other people in this thread who feel it is not related to V4)

So there's as much info as I can provide and I'll keep paying attention to this thread so we can solve it hopefully sooner than later.  If I loose those .pz3s I'm gonna be really unhappy.