Some peculiar problems we (and others) may face while implementing Drupal or maintaining the site.

Whenever you get an error, basic tip:-
(1) do not panic
(2) right click, copy the error message or a part of it, usually the beginning part
(3) paste the error (extract) message into Google search
(4) also paste the error message into Drupal.org's search box.
(5) results are bound to appear. This means you are not alone. Patiently look through the search results which are usually forum threads and you may find your answer there.