[R-SIG-Mac] Error updating packages

[Ista Zahn]

Hi,
When I try to update packages I get an error saying

Error: cannot remove prior installation of package ‘boot’

This happens both when I use the GUI and when I issue  
update.packages() from the command prompt. Does anyone know what the  
problem might be? I'm running R 2.6.2 on OS X 10.5.2.

Thanks,
Ista