[Orgmode] Column view does not work any more in agenda buffer?

[Wanrong Lin]

Hi,

I just installed version 5.13, and found column view does not work 
anymore in agenda buffer (with key stroke "C-c C-x C-c"). I got an error 
message in the mini-buffer saying "Wrong type argument: stringp, nil". 
Does anybody else see the same thing? Thanks.

Wanrong