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

Summer Products /Routine:
Clarifying: ACV rinses, Suave Professional Men Deep Clean Peppermint
Low Poo: Renpure Luxurious Argan Oil
Co-washes: VO5 Kiwi Lime Squeeze or Strawberries & Cream
RO: VO5 KLS or S&C, Cure Care
LI (if needed): VO5 S&C, VO5 SC, Cure Care
Stylers: FSG, AIF,
Tresemme Flawless Curls Bouncy Curls gel
PT: IAGirl's (link) as needed