Don't guess. Look at the "details" for the PR1.3 update in app manager. Next to the tab that says you need to use Nokia update manager is another tab with "Problems" as a title.

This tab lists all packages that prevent an OTA update. Make a list of these and close app manager.

Then open xterm and type "sudo gainroot" (you do have the rootsh package, right ? :-)

Then for each package in your list, type "apt-get remove <package-name>" and confirm.

When you're done, go back to app manager and this time it should let you install OTA.

This just worked for me, found it in the huge PR1.3 thread...