If your using Photopost 4.8.6 and have VB3 integration set to On then it would grab your cookie settings from VB3 if you have things set up.
Your running 4.8 which is why it is not set up right which means you have not set cookies right.
I would if I where you upgrade since 4.8.6 is a security fix also
If you do not want to upgrade your cookie settings are this
cookie domain blank
cookie prefix bb
cookie path /
Then also enter your correct VB
License in the config where it tells you to