I just went through a similar thing where I couldn't export an mp3 in Cubase 4, but knew I was doing it right because I was able to do it in Cubase SX3.
In my case it was a corrupt file in my Cubase Preferences. I had to reinstall the program (I installed an updated version) and then I was able to drag my old Key Commands and Templates over so I didn't have to do them over from scratch.
Even doing that, it was a huge pia and I'm still getting the bugs out of it, but I am now able to save an mp3.
If you do this, I would advise copying your entire Preferences folder to another location before you reinstall.
These type of stupid time wasters will go one forever as long as these software companies keep issuing upgrade after upgrade, and I never want any of the stuff they add.
What they should do, IMA(arrogant)O, is burn a version of Cubase to the dongle (shit, they sell 4GB flashdrives for $10 what's the problem?) and it always loads instantly and it never crashes. All the upgrades would be software plug ins.
They should do the same thing with the computer's OS. Windows XP was fine. OS 9.2.2 was fine. I haven't wanted or needed one thing they've added with all these upgrades after upgardes. I only keep upgrading hoping they will eventually live up to their original promise.
The most amazing thing is that they have sucked everybody into thinking that all these constant upgrades are "the only way to do it" and are necessary.
Thanx