gmp: /opt/local/include/gmp.h already exists and does not belong to a registered port

[jerome.scaph@…]

after a "sudo port upgrade outdated" this occur and stop with error (osx-10.6.8 i386):

--->  Computing dependencies for nettle
--->  Dependencies to be installed: gmp
--->  Activating gmp @5.0.5_0+universal
Error: org.macports.activate for port gmp returned: Image error: /opt/local/include/gmp.h already exists and does not belong to a registered port.  Unable to activate port gmp. Use 'port -f activate gmp' to force the activation.
Error: Failed to install gmp
Please see the log file for port gmp for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_ports_devel_gmp/gmp/main.log
Error: The following dependencies were not installed: gmp
Error: Problem while installing nettle
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets

[jerome.scaph@…]

main.log file concerned of gmp failed

[ryandesign (Ryan Carsten Schmidt)]

Why does /opt/local/include/gmp.h already exist on your system? What other files do you have installed in /opt/local that were not put there by MacPorts?

[jerome.scaph@…]

because i try to update and clean my port... but, i can not understand the finality of the question. maybe rvm do this or other... i just a end user, not an expert hacker/policeman. so i report you a disfonctionnement of the port command as ask on the console retrun message. thank you.

[jerome.scaph@…]

so... i would like also to write that, i no understand nothing about osx organisation OS. I see that my osx-10.6.8 is on i386 arch, and i see many x86_6' arch, some other noarch, some othert i386... so for me, there is absolutly nothing logical inside this. Why not all in the same arch construction ?