Sorry - but more details needs to be given to help you accurately.
Could it possibly be the file type? Maybe you need to convert the fraps file from it's format to a supported type needed in windows 8.
For instance if your fraps file is a .avi and you need to have a mpeg4 to import it into Movie Maker. Or vice versa. You need a software that can convert your files to the type you need. Like the software "Any Video Converter Free Version"
I am not too familiar with Windows 8 and I quit using Movie Maker long ago. So this is just a guess with some issues I have encountered in the past.
Hope you can get it figured out.