PHP.INI file is not configured correctly

I have a project that is based in PHP with Expression 4. When I am about to preview my page on my browser, the error below pops up. This error is new to me and I need some help on resolving this. I have spent so much of my time working on this project and I do not want to lose anything and start from the scratch again. Please let me know what will happen if I click on the Yes button in the error message.

Microsoft Expression Web
The php.ini file is not configured correctly. Would you like Expression Web to configure this file?
Yes No
