I assume you are a premium member, and have set up a password? Otherwise, you will not be able to use the premium feed at all
I am a premium member, I use Juice, and it often shows this error, but it does not interfere with your ability to download. 
Are you using " 
http://www.japanesepod101.com/premium_feed/feed.xml " as your Juice URL ?
By the way, when do you get Juice up and running, you will find it has a few other minor issues. The name of mp3,mv4 files once downloaded will be massively long, having a tail of lots of letters and numbers. Here is an example that I downloaded only a few minutes ago.
V_S2L23_121010_jpod10_sid_c9fa9ea8c7c479dff4934f56e8058f11_l_sid_24384_l_eid__l_mid_2319385_dopvhost_hw_libsyn_com_doppl_81ce5623ccca52c2cc9a52c21d5f5588_dopsig_a572945a6032ffcf362f3ee3ee5280d0.m4v
It's not much of a problem, I just delete all the after "jpod".   mP3 files are now appearing as " .mp3.partial ", and you have to remove the " .partial " as well. Annoying things to fix, but at least the lessons titles are not truncated like Itunes does.