Scripting Now-Up-To-Date

Does anyone know how to write an Applescript that will set the event description? I actually want to copy the contents of the clipboard to the event description.

Just to see if the event description could be set at all, I tried this:

tell application “Now Up-To-Date”
tell event 1 of category 1 of document 1
set description to “This is the event description”
end tell
end tell

I get the following error:

Now Up-To-Date got an error: Can’t set description of event 1 of category 1 of document 1 to “This is the event description”

Any help much appreciated. I am using system OS X v. 10.6.1