I am having the same problem. I contacted support using the chat option. They told me to do a "soft" reset, which did't fix the problem. She told me wait 24 to 72 hrs. and try again.
I'm having the same problem--going on 3 weeks now and I have been able to view my wishlist twice and then I can't see it anymore. VERY frustrated!
There are several threads out there addressing this same issue and I am going to post this response on every one of them! I am really pissed about this issue, especially since it has obviously been a problem for a very long time. Even if B&N won't admit it.
I had the same problem with my ~1 year old Nook Color about 2 months ago. I took it into a store, and the employee claimed she had never heard of this problem before. After great wringing of hands, she said the only solution was to reset the Nook. I reluctantly agreed; I use the Wishlist to not only show new books I am interested in, but to queue up the next installment of many series I am reading.
After a couple of weeks of FINALLY reassembling my wishlist, my list of internet bookmarks, and my shelves, the Wishlist started acting up again, then finally crapped out. This time I tried the chat support option. The support hack I spoke to spent 20 minutes going through all the 'usual' solutions: turn it off then turn it on, turn it off for 10 seconds then turn it on, blah, blah, blah he said that this is a recurring server problem that Tech is 'working on'. He couldn't say how long they have been working on it, or how long until they expected to solve it. He said the only he could suggest was to reset it and hope they solve the problem before the Wishlist craps out again. I asked him, if I choose not to reset and live without the Wishlist on the Nook, how would I know when the problem was fixed, he said try it every couple of days!!! Seems to me this is not a day-to-day problem.
So now I am left using the Nook wishlist online, which is a GREAT pain in the butt, and combined with B&N's policy of advertising 50% off books that aren't actually half their regularly advertised price and crappy deceptive support, wishing I had bought a Kindle.