Why doesnt the video allow me 2 save 2 disc?

im using microsoft video maker 1.2 and i ran into a tiny problem...

can someone tell me what's wrong? windows XP wont allow me to save onto a
disk and every time i reach the last step of the saving process, the computer
will say the source files are gone or something ( every source file is
there...i checked and there are enough space on the disc im trying 2 save 2)
..... i can save movies as a project ( as a .msmvm (or something like that)
file)...