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In admin->system admin->preferences->General Settings
ebug mode => set to PHP Debug.
As I see on a previous post, you are running 2.0.5.1
This version has a disabled XoopsErrorHandler, which means, as far as I know, that not every warning is outputted.
(Maybe someone can correct me, if I'm wrong)
Just to be sure.
Have you been at admin->system admin->groups.
E.g. click on the Search block link (within the field Block Access Rights). This opens the 'Edit a block' for the search block. In the field 'Visible in' is 'All Pages' selected?
(Or at least 'Top Page'?).
(Selected means white chars on blue background)
If yes... no more ideas then.