A couple of MacPorts errors I just encountered:
Error: Unable to execute port: can't read "frameworks_dir": no such variable
I had version 1.6 and it seems the recommendation to fix this is to update to 1.7 (via port selfupdate). I started port in interactive mode, ran selfupdate, then tried my install again and got:
Error: Unable to open port: can't read "porturl": no such variable
I wasn't sure if it was necessary, so I ran 'sync' at this point. The install then failed with:
Error: Unable to execute port: can't read "PortInfo(name)": no such element in array
Couldn't find any info about that online, so on a lark I exited port and restarted it, after which the install proceeded.