Thanks, With dvdinfo, I've set my dvd nec2500 to default -ROM booktype. Dvd info also tell me that I can make another 499 changes before the flash memory stops working. Since it works fine now, there's no need to do so.
In Nero the booktype option you mentioned, was not there. But after having set it in dvdinfo to -rom ev'ry works fine.
Perhaps nice for some people to know,
I changed firmware from an OEM version of Fujitsu-Siemens to Mad-dog hacked firmware version 1.08v3-2 using a special flash tool. http://www.herrie.org/utilflash.html
Now I'm able to burn double layer dvd's and of course RPC1, and bitsetting.