That directory is usually created in the installation process. Was the database created properly? You could manually copy the webassist directory from the install/webassist/ directory if your database was created properly... however I think it must have created the webassist directory if you are able to get to that point before having problems.
Most likely this is a permissions problem with the /webassist/ directory that was created on the server. Try changing the permissions on that directory from '777' to '755'... that has helped others that have reported the same issue.
Did this help? Tips are appreciated...
