DON'T use any drape frames (they can't be edited).
DON'T parent the towel...(or if you need to to move both the figure and the towel together before the anim/clothify stuff starts - do that all in frame 1 then re-parent the towel to "Universe")
Then save the scene (as a PZ3 file) - it'll save you time later...

Exit Poser, restart. Load the saved file (this is just to free up memory if you're like me and have limited memory). And, of course, it gives you a re-start point if you need to break off a session (for sleep-type reasons..

Do it in 2 parts.
Part 1 - drop the towel over the figure (without changing the figure's pose) in the cloth room. Select the best frame (for a still), export the towel as a .obj.
Part 2 - Re-load saved PZ3 file, delete the existing towel, load the saved (now draped) towel. Move to (eg) frame 20, pose the figure. Return to frame 1 and clothify the "draped" towel. Run simulation...

In the 2nd part, you may get problems with "over-run" in the character's posing. This can be solved in the animation editor by selecting the end pose and applying "break spline" or by making the animation linear..

If you don't know what I'm talking about, I apologise, and I (or someone with more knowledge) will try to explain in more detail..

(But right now, my "explanation" brain-cell is undergoing a massive DUH! convusion...)

But hope that helps, anyway...

Cheers,
Diolma

Do you want to create a still or an animation?