sudo port selfupdate
I've found that this is the most common fix for a failed port install. For example, today, I had the following error when trying to upgrade Subversion:
> sudo port upgrade subversion
---> Building sqlite3 with target all
Error: Target org.macports.build returned: shell command " cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_databases_sqlite3/work/sqlite-3.6.1" && gnumake all " returned error 1
Command output: sh: line 0: cd: /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_databases_sqlite3/work/sqlite-3.6.1: No such file or directory
Sometimes a port clean is also required.
