It really looks like what happens to me when I set up a custom path server and forget where I put it. I've found that

[CODE]tmux -S /path/to/socket/socket session attach [/CODE]

works pretty well. I run Linux, so it might still work for you.

[CODE]ps -aux [/CODE] should tell you the command that created the tmux session in the first place.

Also look to see if the command uses -S or -L... Use which ever flag that created the season, plus the path to your socket. Add session name, separated with a space at the end for good luck.

I have shell scripts set up my tmux sessions and it can be easy to forget the specifics. Tmux won't know to look somewhere other than the default without the -S or the -L switch on.