If you suffer from this problem when trying to view the Adobe preferences, then drag the Multimedia.acroplugin folder from the /Applications/Adobe\ Reader\ 9/Adobe\ Reader/Contents/Plug-ins folder.
To do this from the Finder, control- or right-click on the Adobe Reader application icon, then choose "Show Package Contents" then navigate to the Contents->Plug-ins folder.
Drag the Multimedia.acroplugin folder to the Desktop or some other place, so that you can put it back later, when you desire to see an annoying error.
As for why this happens?
I don't have any clue, but I got the idea from looking at /var/log/system.log and clicking on Preferences in the Adobe Reader application.
Now that that's settled, I'd like to know why I can't print because the Comments.acroplugin plug-in doesn't load.
For the reference of the Adobe software developers on this list who may have been stumped about this problem, I am using a Macbook with 32-bit EFI firmware, the 32-bit kernel, with an extended hfs case-sensitive journaled file system under Mac OS 10.5.8.
Please ask the Mac team to see if there is some problem that could be related to these details.
As for Mac users in general who are experiencing this problem, please report your system model and software version as comments to this thread so that we they can include/exclude certain factors to root out these problems.
extended hfs case-sensitive journaled file system
This is the root of your problem. No Adobe software is designed or supported for use on the case-sensitve file system. Apple doesn't recommend this file system for anything but the OS X Server.