This window signifies that your PDF is trying to connect with the
comments repository.So it is bound to pop up , almost everytime you open
the PDF.However if you accidently make a typo while entering comments,
this window will keep re appearing, even if you enter the right
credential in successive attempts.The only workaround is to kill the
collabSync service.however try the latest version of Acrobat / reader
i.e. 11.0.6, i believe the problem is fixed there.