Thank you Alex,
But that isn't the case. I am sure the path is right. I also, thought this is the problem at first. Right now I have the file in my src folder together with the flex file.
I solve the problem by adding font manager to the complier.
In the flex builder, project properties -> Flex complier -> additional complier arguments -> -managers flash.fonts.AFEFontManager
Dear I am facing the same problem and using Apache ANT from command prompt for compilation instead of flex builder. Could you please guide me how can I add additional compiler arguments using command prompt?