virtual dub problem

[gymrat]

Hi
i have been using virtual dub to join 2 mpg files together, but today i tryed to do the same..i open my first mpg file and load it into VD then i click on "append segement" and then save...but for some reason the "append segement" is now greyed out.
can anyone tell me why this could have happened and what i need to do to resolve this?

Thanks

Gymrat