I am battling this same issue right now. New install, Photopost itself installed fine when I did that a couple weeks ago. Classifieds won't accept the admin login. I have my cookie prefix/domain blank (because I left it black in Photopost and it works with no issues). I added bb/domain info for the heck of it and same thing happens. I verified the VB
license # in PHPMyadmin and it is all fine.
Going to try and reinstall...
EDIT: Ok I reinstalled, triple checked all settings. Cleared cookies, you name it. I even renamed config-intc to config-int at one point since the setup process referred to the file as config-int - nothing is letting me log into the admin. It says it works but then dumps me to the main classified screen without the user/pass being retained. I've tried in both Firefox (what I normally use) and IE (which I never use). same result.
Also, when it does this, if I try to go back to the main forum I have to reenter in my user/pass there. Once I enter it, I can go to Photopost (the gallery) and it retains fine, only classifieds is muffing up.