Why can't I encode in DivX after upgrading to DivX6?

This is becuase PowerEncoder 1.0 and 1.5 do not support DivX6.

CyberLink often works together with other software developers, and DivX is one of them. We included the DivX codec in our software to provide end-users with the ability to encode in DivX for no additional charge. However, the DivX version that is included in PowerEncoder MPEG-4 is an older version and the new DivX6 version has new features that are not backward compatible.

If you already have upgraded to DivX6 you will not be able to encode in DivX from within PowerEncoder. Right now, the only solution is to uninstall DivX6, and then reinstall PowerEncoder.