I'm having a similar issue, but it's site-wide. When I'm on the main CurlTalk page and I click the Sign In link in the top black bar, it never shows me as signed, nor does it give me any kind of error. However, in the main body of the CurlTalk page, it'll show "Welcome, Geek_Chic" and I'm able to post threads, get into the UserCP, etc. as if I'm logged in.

If I use the black bar to sign in on the nc.com homepage, it shows me as signed in afterward. If I then click to go to the Frizz Forecast, an article,products section, or CurlTalk, the black bar shows me as signed out, though I can still post in CurlTalk as if I was signed in.

I use Windows 7 and Firefox, if that helps in diagnosing.
CG since 11/2011
2c /3a F /Mii, low porosity

Spring Products /Routine:
Clarifying: Herbal Essences Tealightfully Clean
Low Poo: Renpure Luxurious Argan Oil
Co-washes: Suave Naturals Tropical Coconut or Daily Clarifying
RO:
Tresemme Expert Selection Perfectly (un)Done, Cure Care, Suave Tropical Coconut or Daily Clarifying
LI (if needed):V05 Kiwi Lime Squeeze, V05 Strawbery
Renpure Brazilian Keratin Straightening (old formula), Cure Care
Stylers: LALSG
PT: IAGirl's as needed