This happens for specific fonts you convert to @font-face using CodeAndMore @font-face kit generator.

(in the example it is Myriad Pro Regular but it could be any fonts with the same CSS3111 error)

Most of times, this relates to invalid font info which can be fixed using FontForge.

Download FontForge, http://sourceforge.net/projects/fontforge/
Then install, open your font, visit menu Elements , FontInfo

As you can see it does not contain same information. Copy Fontname then paste in Family Name, then click OK

(In the example, it is Vista Sans OT Regular, but it could be any fonts with different font name and family name)

Update July 29 2013

For some fonts you may need to change in TTF Names / English (US) – Family to the same font name before generate font.

Update Oct 10 2013

The solution (for above things, in stroked text) is now integrated directly in the generator. Most of  the time you can just upload your font here without using FontForge.

Update Nov 13 2013

For some fonts you will need to remove all languages out of English (US). In TTF Names, choose the item with different language, and click Delete.

Then click File / Generate Fonts
Choose Open Type (if you open an Open Type font), True Type (if you open a True Type font, but that does not matter much because CodeAndMore @font-face generator can work with both) and save, if any warnings just proceed, save anyway etc.

Use that generated font file to convert and test result.

Enjoy fixed EOT file on IE7, IE8.