Problem with portupgrade

[Phillip Ledger]

i have been trying to get portupgrade working, however everything i try 
to run it im getting an error with the portsdb. now i have tryed to 
rebuild it as requested initaly by portupgrade but im still getting an error

portupgrade -aRr
[missing key: categories] [Updating the portsdb <format:bdb_btree> in 
/var/tmp ... - 16413 port entries found 
.........1000.........2000.........3000.........4000.........5000.........6000.........7000.........8000.........9000.........10000.........11000.........12000.........13000.........14000.........15000.........16000.... 
..... done]
missing key: categories: Cannot read the portsdb!
/usr/local/lib/ruby/site_ruby/1.8/portsdb.rb:548:in `open_db': database 
file error (PortsDB::DBError)
        from /usr/local/lib/ruby/site_ruby/1.8/portsdb.rb:702:in `port'
        from /usr/local/lib/ruby/site_ruby/1.8/portsdb.rb:890:in 
`all_depends_list'
        from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:809:in `tsort_build'
        from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:801:in `each'
        from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:801:in `tsort_build'
        from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:823:in `sort_build'
        from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:827:in `sort_build!'
        from /usr/local/sbin/portupgrade:721:in `main'
        from /usr/local/lib/ruby/1.8/optparse.rb:755:in `initialize'
        from /usr/local/sbin/portupgrade:220:in `new'
        from /usr/local/sbin/portupgrade:220:in `main'
        from /usr/local/sbin/portupgrade:2084


any idea whats causeing the issue or how to fix it?