, yesterday I had the same issue as you and was not able to find an answer to my problem on the internet. So I try a few things and that's work for me
First, I desinstall multiman then backup my internal hdd on a usb device (system option).
After that I boot my PS3 in recovery mode. I made a "restore file system" which was unable to repair and ask me to format my hdd. After that I try reinstalling multiman but the problem of connection was still there.
So desinstall multiman again, reboot in recovery mode and try to rebuild the database. Again no solution for my problem.
So I try one last thing in the recovery mode : Restore PS3 system. And miracle the problem is solved. After reinstalling multiman base 2.7.01 I was able to update to 2.7.04 in multiman. I restore my hdd with my backup and now all work fine, like always.
Hope some of you could find that usefull