entity reference field setting(edit) shows a blank page

Hello all,
I need your help.
I installed both entity reference and required modules(entity api & chaos tools)
I succeeded to create a entity reference field, but failed to edit the field settings.
In the Manage Field tap, when I click "edit" link of the newly created entity reference field, it shows a blank page.
Do NOTHING.... so disappointed
I attached a blank page screenshots.

Anyone of you have a way to solve this issue?

Thanks