"No panel found..." in a reference load definition

I'm trying to set up a reference load case that has a number of one-way loads. I added the one-way loads to the reference load definition by simply copying some existing dead loads. However, when I run the model, I get a warning that says WARNING: NO PANEL FOUND FOR A ONE WAY LOAD GENERATION.

Here's a shortened version of my reference load definition:

DEFINE REFERENCE LOADS
LOAD R1 LOADTYPE Dead TITLE REF LOAD 1
SELFWEIGHT Y -1
ONEWAY LOAD
YRANGE 231.917 231.917 ONE -0.01 XRANGE 63 90.5 ZRANGE 55.5 58.5
END DEFINE REFERENCE LOADS

Any ideas?