The latest update to Passwords Plus is compatible with both Palm Desktop 4.2.1 and Mark/Space The Missing Sync (you'll need version 6.0.2).
The Passwords Plus patch download link and full installation directions can be found on the DataViz website.
I'm happy to see that DataViz is still actively supporting their software on both the Palm OS and Macintosh platforms. It shows that DataViz is still committed to their customers who are part of the Palm and Apple user communities. By making this upgrade available, DataViz has helped make my transition back to the Macintosh (from Windows XP) a little bit easier.