yes,
run for tha hills!!!
Seriously, close your board, download this file and rename the extension to .pl instead of .txt
https://www.ubbdev.com/hacks/deletehacklines.txt Upload it in ascii to your ubbcgi directory, set permissions to 755 or 777, type the location into your browser and run it. It will give you a text readout of what it is doing, which is going through your member files and deleting the extra profile fields from your v5 ubb.
Then, run the ubb_upgrade.cgi file in your ubbcgi directory to properly upgrade your v5 files, your old 18 forums will appear then. If it doesn't run, and says that you've already upgraded, then come back here, there'll be a sub in ubb_upgrade.cgi you'll need to remove to force it to run.
Good luck, and make backups of your members directory first.