I thought that might have been the problem, but it isn't, as while I was away, more PPS LLR downloaded, as well as PPS Sieve. So I'm able to get WUs for both CPU and GPU without any problem - just can't get anything from WOO LLR.
I am going to try the following: Setting PG to No New Tasks and letting PG empty out of my Tasks list. Then I'm going in and selecting only WOO LLR and see if I can get something to download that way.
I know it's not a problem with the program, as the program that PPS LLR and WOO LLR are the same 6.09, and since it worked with the last challenge, that rules out the possibility of a faulty program on my rig.
I'd hate to have to keep myself out of crunching PG units until the next challenge rolls around, so I can compete in it, versus crunching for regular credit.
Also, I think the stipulation on how to get WUs, like mentioned below, is no longer in effect. I read a forum posting a while back saying that the problem has been resolved.