Check "Settings -> Global variables -> cb_release_type" and make sure the base-entry has either an allowed gcc-flag (like "-g") or a space.
Don't leave it empty, or C::B replaces it with the string "(invalid)" after asking you if you really want to save an invalid global variable.
Also check the "cb"-variable, it should point to the root of C::B's sources on windows (if I remember correctly).