I am getting the following warning when previewing a webpage I'm working on -

Click image for larger version.  Name: Warning Font.jpg  Views: 141  Size: 76.0 KB  ID: 99675

Obviously the font is installed or how would it be in my design. That leaves the matter of the format. The font displays correctly in Xara. It is an otf font. This is a font which I purchased and which is licensed to use on a website. I also have a version of this font which is a webfont and is ttf. I tried to use this font instead but windows doesn't recognize it as a ttf font for some reason. I understand that webfonts need to be referenced in the css sheet but can't see how to do this from Xara.
Any thoughts would be appreciated. I not quite sure why this has to be so convoluted.
Thanks in advance.
Kris