I think I found the cause ...
I use CKEditor for the back-end and have
not installed TinyMCE via the Package Manager. Instead I manually installed (independent of MODX) the standalone version of Tiny along with Responsive Filemanager for use with NP on the front. In NP v2.0.2 this setup works beautifully, but it clearly breaks in v2.1.
To test it I removed,
&initrte=`1`
&rtcontent=`1`
&which_editor=`TinyMCE`
from the NP call the NP page/form once again renders fine, but obviously without Rich Text Editing.
I don't know if this is a bug with NP 2.1 or an error on my end, but for the time being it seems I can’t use the new NP.
[ed. note: todd.b last edited this post 11 years, 6 months ago.]