I am using Emacs 24.4 and org-mode 8.2.10 (I can't understand why I can't update it to the last version 8.3.1. My version is the last in ELPA but when I ask for org-version I get 8.2.10).
The fact is that now I cannot export any org file to any type of file. The error message is Symbol's value as variable is void: org-planning-line-re.
One suggestion would be to reinstall Org from a new instance of emacs in which your current copy of Org is not loaded.
It seems, based on your description, that Org 8.3.1 was installed from Elpa while your existing copy of Org (8.2.10) was active, which resulted in a corrupted installation.