Sorry for the delay in replying (I forgot to turn on email notification).
The files are .avi. I have noticed that in other programs of the suite (Burning ROM and Nero Express) I get the error message “unsupported file format”. The thing is I used to be able to burn all the .avi files I had and I am still able to watch them on the various players I have (VLC [my favourite], ShowTime, DivX), except for Windows Media Player which has stopped playing almost everything, also reporting that the file is of an unsupported format.
What I have read around the internet suggests I am missing a codec or two but I don’t understand how considering that I am still able to play .avi files.
Finally, Nero still burns other file types such as .mpg.
Thanks for any help.