Hi Sangsom,
What you changed in the Common.config? What you want to achieve with it?
Try add a textbox in your page, andd type the content below into the textbox, then get the value and save it into the db, does it get any problem? If you get the same problem with it, then you should check your db setting of the insert code, why it does not work with the content like that. this just the simple html content.
<span style="font-family: 'Times New Roman'; ">test</span>
Regards,
Ken