Can you link to the exact extension you are using? There seems to be miscellaneous ways of getting math functions to a mediawiki site.
Just as Wikkii said, I use the default extension in the farmer wikis to invoke a math expression. (command like "<math></math>")
Thank you for the notice, I have made the required changes according to the instructions for the public mimeTeX service.
Thank you Wikkii, it's OK now. But I have a question on mind. After your change, I still can see the same warning message on my page, even if I cleaned all the cached files and cookies in my browser. However, if I move my page to new title or copy all the contents to a new page, then math expressions will be showed as good as before.
That's a little bit strange, isn't it?
Anyway, now everything is in good situation and thanks again!