Dvd burning using nerocmd stops after a few writes


I have written a script to burn a multi session dvd using batch files and nerocmd(Nero 7).
This script is executed once a day in the evening to take a backup of a MS Access database. The drive being used to write is an external sony nec dvd writer. At the end of the day I shut down my PC.

Please find the commands that I use to burn the dvd below.

For the first write:

nerocmd --write --real --drivename f --close_session --iso Bkup --recursive --disable_eject --media_type media_dvd_p_rw %newFldr%

For every successive writes:

nerocmd --write --real --drivename f --import --close_session --iso Bkup --recursive --disable_eject --media_type media_dvd_p_rw %newFldr%

where %newFldr% holds the path of the folder to be written.

This script works properly for 2-3 or a maximum of 5 writes. Then the burning will not happen. When I checked the disc, the total size written is hardly 700-800MB. But the disc has been marked as full and no more data can be written to it unless I erase the entire disc and re-write whatever I had written earlier. It also says that the previously detected media was a DVD-RW and requested media is DVD-R/RW.

Because of this I am forced to take a backup of whatever I write to the dvd on my hard disk also.

Could somebody please help me out? Thanks in advance