I created a simple poncho in Truspace 3 and exported it to a wavefront OBJ file.  It imports ok, but it's totally flat.  So I put it in position on my character and "clothify" it, and start the draping process.

The drape starts to work, goes about 9 of 30 frames, and then reverts back to flat.  I told the drape to go 30 frames, but the frame counter keeps on going.  I stopped it at "draping 130".    Grr.

Does anyone know what's happening here?

That's one of the things that is so great about Poser 6, the cloth room is so much more improved.
Not sure what I can do to help you on Poser 5, the cloth room worked so lousy I gave up
using it.  It took a while to go back using it when I got Poser 6, and I was shocked at how
easy, fast, and reliable the cloth room is in Poser 6.  Now I much prefer it to using
conforming clothes.

It's a bug. Poser 6 does it too, but not very often.
Usually it means Poser don't like your simulation settings (clothing settings); Change them and try again, it should work.

any ideas which settings I should start with?

Unfortunately not. When this happens I usually start all over, so I never found the culprit.

To start use the default settings, just adapt resistances depending on the cloth type (leather doesn't bend like satin). Don't use values too extreme, else Poser will do some really strange things. Run the simulation, check the result and adapt values till you get something which looks like it should. It helps having a fast computer and a simple scene; What I do is clothify in an empty scene, spawn a morph target, save the figure and her clothified cloth in the library, and insert it from there into the scene. Of course the simulation is lost (good thing, economizes memory), but since you have your morph it doesn't matter.

I also remember that Poser 5's Cloth Room  was a little quirky; Poser 6 was buggy, but Poser 6 SR2 is stable at last. YMMV.

Maybe I'll just wait for Poser 7.  I can't beleive they released a buggy cloth room and didn't fix it in a patch.  I hate this trend in software companies.  Anything to keep you shelling out $500 every 2-3 years.

Normally that occurs when the cloth is intersecting something or itself.

Attached Link: nerd 3d article on cloth draping

look at the above link...

Hi, commander..

1. You don't need to parent the cloth to the figure. That's only needed if you decide to save the prop to the library (and if you want it to automatically go to the correct position when you re-load it from  the library - see extra notes below).

2. Try the following... (assuming you modelled your poncho as a flat cloth - definitely recommended)..
    Start a new Poser session.
    Load your figure and zero it (not the default position, the zero pose).
    Import the (flat) poncho.
    Position it (if necessary) such that it is above the shoulders, but below the chin.
    Ensure that the pocho is NOT intersecting with the figure  anywhere.
    Scale it in x and z if necessary.
    (SAVE as PZ3) - just in case you need to restart..

 Enter the cloth room, clothify  the poncho, collide against your figure, (DON'T bother with any "drape frames", they just get in the way, set them to zero).
 Run the sim. (30 frames should be more than enough..)

Assuming that worked -
 Find the best (most natural for a zero-posed figure, cloth falling naturally) frame of the sim, and export the cloth as .obj. (under new name - eg: PonchoDraped). DON'T CHECK ANYTHING ON EXPORT.
 Exit Poser (to free up memory, mostly), and restart it.
 Load Figure (and zeroise it).
 Load PonchDraped (DON'T CHECK ANYTHING ON IMPORT).
 The Poncho should now fit the figure in the "zeroised" position. All the above is, really, the easiest way to get to a starting position. Once you get used to using it, it becomes second nature..

At this point, if you think you're going to use the poncho again, you could parent it and save it to the props library. (BTW - What parenting does is move the prop (ie Poncho) to the correct position on the figure when loaded from the library, and moves the prop together with the figure if you move the figure in the studio. There are other effects don't affect this discussion, except to say that if the pose moves the figure, then parenting can get in the way of the cloth moving correctly..)

OK. You have figure (in zero position) and fitting Poncho.
Next...
 Go to frame 15 - 20 (it depends, 15 is probably more than enough for a poncho) and pose the figure.
 Return to frame 1 (not absolutely necessary, but avoids confusion).
 back to Cloth Room, clothify PonchoDraped, collide against figure etc and let it rip...

Anyway, that's the way I do it..... there's probably a better method but I haven't found it yet.
Not that I've looked too hard - it works for me, doesn't cause me much trouble, so unless someone comes up wit a super-streamlined approach I'll keep using it..
 
Hope that helps,

Cheers,
Diolma

ok, I figured it out...

First, the way Truespace clipped the neck hole out of the cloth left long triangles from the hole to the corners.these acted like stiff poles when the drape was happening.  I wrote a Delphi program (because I can't clip a mesh in truespace for some reason) that created the mesh I wanted and it all worked fine.

Thanks everyone for your help.