I have encountered this problem when I test the SyntaxHighlighterPlus plugin for this blog. This plugin cant work properly with my theme although I have follow 100% instructions from the author. You can see the screenshot below .
To solve the problem, I just copy the code from
/wp-content/plugins/syntaxhighlighter-plus/shlfiles and paste it to my current theme css. Thats the way to solve it..hah.