Unix never lies. It realy means the device is busy. It can have several causes. Your current working directory resides on the mounted CD. Or maybe your previous ksh still resides in there. fuser -cu /SD_CDROM should tell you more. This shows you the current runnning prcesses on this FS. ps -ef and than look for possible processes running on this FS might clear out some as well.
It is very important to first make sure all processes have stopped on this FS before stoppping and restarting mountd.
I have seen problems on Soalris often (especially with Oracle CDs for some reason) where vold gets messed up and no matter what you do you cannot eject the CD. There are 2 options I use: