I found a workaround but its really messy since you lose all your settings.
go to:
:\Steam\steamapps\common\Eve Online\SharedCache\sisi
open “start.ini” change line
server = Tranquility to server = Singularity
save and close
goto
C:\Steam\steamapps\common\Eve Online\SharedCache\sisi\bin
start evefile.exe
and you can join SiSi again.