Merge the login process of two PHP based programs (continuance of previous programmers work)

I recently posted a project to merge the login process of two php based programs: a freelancer script and the Questions and Answers script. At the completion of that project, the hope was to allow users to register and/or login in the freelancer script, and have access to both the freelancer and Q&A script. In other words, once the user was registered and logged in freelancer script, they were also logged into the Q&A script, without having
to relogin or register in the Q&A script. I selected a programmer who came close to accomplihing this task. The user registers in the freelancer script, and those login credentials can be used in the Q&A script. However, to use the Q&A script, they have to login in again. I want to avoid this repetition. The programmer states that it cannot be done because the authentication process in the Q&A script is encrypted, and there is no way to carry the user session from the freelancer script to the Q&A script (or something to that affect). However, i'd like a second opinion, as i've seen this accomplished before. So, in summary, this project is to finish the work of the first programmer; to accomplish the task of having my users logged into both the freelancer script and Q&A script after only having to login into the freelancer script.

Please message me with any questions or further clarification.
Freelancer site is at: www.legalally.com/marketplace
Q&A site is at: www.legalally.com/ask
To see the problem which I speak of, register at the freelancer site, then visit the Q&A site and attempt to ask a question. You'll have to login again.