in the name of ALLAH
How do I burn a DVD+RW utilizing NeroCmd.exe?
First command:
nerocmd --write --real --drivename I --dvd --close_session --iso-mode2 --disable_eject --error_log f:\NeroCMD.LOG --no_user_interaction --iso TestIso f:\test\a.rar

Second command:
nerocmd --write --real --drivename I --dvd --import --close_session --detect_non_empty_disc --iso-mode2 --disable_eject --error_log f:\NeroCMD.LOG --no_user_interaction --iso TestIso f:\test\b.rar

both of commands have been executed successfully !
but a.rar is visible in explorer and b.rar isNOT visible in explorer !!!

i don't have the solution to your problem, but it seems many people post in this forum but few get any replies - so i'll give you my suggestion:

try changing that --dvd switch. i think there are other options listed in the docs, such as "--media_type media_dvd-rw"

you should also test your steps using the normal nero gui and see if both sessions appear correctly. unfortunately you'll have to waste a couple of discs until you get it write because testing mode (without writing) works only with cdrw's.

p.s. if you find a solution remember to post it here so that others can benefit from it.