Drupal Core 7.14 seems to have introduced/reintroduced an issue with radio form components that do not have a default and are not required/mandatory. In a webform, a select component that is not mandatory and has no default will cause the following error to occur on form submission: "An illegal choice has been detected. Please contact the site administrator." This essentially makes the component required/mandatory even when it should not. This was not the case in Drupal 7.12 and Webform 3.17.
* Install fresh Drupal 7.14 and Webform 3.17
* Create a new Webform node
* Add a select component with everything as default, adding only several Options like 1|One
* Submit the form completely empty
* Error occurs
This issue is being discussed at http://drupal.org/node/811542 starting at post #177.
If this issue is only with Drupal Core and not Webform I apologize for the extra issue. That being said, if I create a new content type, and add a field of type List (Text) and only set Options and no default value or required, the error does not occur on form submission.