Thank you for your reply Sayontan.
You are right. It was Smushit. Disabling it solved the problem.
Hi toneyb, the plug-in doesn’t look anything as nice as in Sean site.
However there is a bug (in the current version, 1.0) in the file “wpppd.php” at line 36, is:
if($Version!='') but should be:
if($Version === FALSE)
You should change that line, then deactivate and activate again.
Hope it helps, and good luck with your cause.