You cannot print self simply by typing po self
on stack frames that you do not have the source code for.
What you need to do is print the correct register.
See more information here: http://www.clarkcox.com/blog/2009/02/04/inspecting-obj-c-parameters-in-gdb/
Make sure to select the correct architecture you are debugging on (i.e. if your binary is 32-bit, 64-bit, arm, simulator, etc).