Hi Hans,
There's a little bug in the script, very easy to fix. Open it in PixInsight with Script Editor. Line #32 of the script is:
#feature-id Utilities > ImageInsert
It should be:
#feature-id Utilities > WriteJPEGWithSizeConstraint
Save the script and regenerate the featured list with Script > Feature Scripts > Regenerate. Now it appears under the Script > Utilities category.
All the best for 2012 to everybody!