I'd like to bring the following little freeware tool for Windows to your attention, with which I was able to burn every Toshiba firmware update successfully, without any problems. The name of the tool is "BurnAtOnce", you will find a download link when you enter that string in the Google search field. Actual version is v0.99.5, downloadable for free from Afterdawn and other freeware sides.
Worth to note is that no special settings were needed to burn the ISO files successfully, I've just chosen the slowest write speed which was offered by the tool (in my case: 4x). I'm using Verbatim CD-R media, never had any problem with home-burned Toshiba firmware CDs that way.
HiVision LDs: 42
HD DVD count: 379 / still 20 on the wishlist