This error occurs when PHP is configured to load modules which it cannot find or which don't work for some reason. I am not super familiar with these types of errors or what 'Unknown' refers to.
I'd try checking your PHP.ini file for the extensions section (any place where it says extension=something.ext):
;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;
;
; If you wish to have an extension loaded automatically, use the following
; syntax:
;
; extension=modulename.extension
;
; For example:
;
; extension=msql.so
;
; Note that it should be the name of the module only; no directory information
; needs to go here. Specify the location of the extension with the
; extension_dir directive above.
You might have a line that says "extension=" without any extension file listed.
Not sure if that'll help.
