I read several things on the net about DVD burning not working with k3b/growisofsand Plextor drives, and I am facing the same issue : OPC failed. Please try writing speed 1x. Fatal error at startup: Input/output error
This doesn't look like authentic growisofs message. It's normally accompanied by numeric code, which might give an extra hint about the problem.
I am using growisofs 5.21, k3b version 0.11.14 and a DVD-R medium.It does not seem to be a firmware problem since burning works fine on the samedrive and media with Nero6.
What media is it? http://fy.chalmers.se/~appro/linux/DVD+RW/ is specific about complementing problem report with dvd+rw-mediainfo output for resulting recording or affected media. And don't make anybody assume things. For example it adviced to try 1x. Did you? Did problem persist? Etc... A.