I think it's time to make that a FAQ.

The link above will take you to where I answered this yesterday. I wish RIM would block the download for that version for all 4.2 devices. The downloadable version of BBmessneger is only for 4.1 OS devices. Please remove that version and reinstall using Desktop Manager and the OS installation for the Pearl. The instructions are in the link above.

I'll get working on a faq for this.