Just like this guy when trying to do $ port selfupdate I'd get errors like:

Selfupdate failed: couldn't open "…/var/db/dports/sources/rsync.rsync.opendarwin.org_dpupdate1/base/dp_version": no such file or directory

The problem is that my macports version is very old and after an rsync dp_version is now in base/config rather than just base. Furthermore because the rsync happens before you check dp_config putting in a symlink or just copying the file over won't work as it gets deleted again before it is checked. The solution I found was to edit /Library/Tcl/darwinports1.0/darwinports.tcl and find this bit of code:

get new darwinports version and write the old version back

set fd [open [file join $dp_base_path dp_version] r] gets$fd dp_version_new close $fd ui_msg "New DarwinPorts base version$dp_version_new"

Then change the first line after the comment so that it reads (i.e. insert 'config'):

get new darwinports version and write the old version back

set fd [open [file join $dp_base_path config dp_version] r] gets$fd dp_version_new close $fd ui_msg "New DarwinPorts base version$dp_version_new"

And hey presto! selfupdate now works.