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

Go To Products /Routine:
Clarifying: Suave Essentials Strawberry
Low Poo: Renpure Luxurious Argan Oil
CO: Suave Essentials Strawberry, V05 Kiwi Lime
RO /LI: Tresemme Perfectly (un)Done, Cure Care, V05 Kiwi Lime Squeeze, Suave Essentials Strawberry, Renpure Brazilian Keratin (old formula)
Stylers: LALSG, AIF, HETT, Suave Professionals Firm Control
PT: IAGirl's as needed