I've complained about this before with no solutions. If I log in with my forum account, I can use the forum with no problems. But I can't use this account for Arduino blogs or trying to submit a project. It always says my credential is invalid. Does anyone else have the same issues? I tried IE and FireFox.
Don't really have any problems here using Chrome.
Try logging in via an incognito/private window. If that solves the problem, kill the cache & cookies in your browsers.
Tried chrome and firefox private window. Logged on at arduino.cc, then when I visited blog, there is no logon. Tried to log on and got "Wrong credentials". Then went to forum link and I was logged on already and logon worked fine.