Your selected input files are resulting in an output file that is too big for the dvd size you have selected.

Two possibilities: 1  you have chosen high quality - which will result in a bigger file - option: choose a lower quality
                                2  you are trying to include too many avis (or whatever) and the overall input size is too big: option make 2 dvd's instead of 1.

The screen you get to after you have selected the files for conversion has a button 'Advanced' - if you click this you will see options to choose the dvd size (4300, 4700 and 8500 I think) and another option to choose quality or speed. Other options also. If you decide to stick with whatever options you already have 'high quality' or 'loads of avi's' you could choose a bigger dvd size, say 4700 instead of 4300 or even choose 8500. After if you have a problem fitting on dvd you could use dvdshrink. You might need to tinker a little, maybe even dvdshrink twice.

Please note that the foregoing assumes that you have 2 folders with 2 sets of dvd files: it just occorred to me you may mean that you have 2 vob files in 1 folder. If this is the case it is again because the output file exceeds the maximum size of a vob file and 2 are needed. You won't see any break when playing back.

I would always advise to use dvd rw disks when experimenting or getting to know new software - saves coasters!