By calling kpagsh you create a new PAG “Process Authentication Group” with an own (new) Credentials Cache, so neither your old Kerberos Tickets nor AFS Token are available. Since your home-directory lies within the AFS, you don't at the moment have access to it → the shell bash can't read the .bashrc in your homedir.

⇒ bash: /afs/math.uni-hamburg.de/users/…/.bashrc: Permission denied

Therefore you need to obtain new credentials that are appropriately tuned to the intended usage by calling kinit.