UBB.threads PHP Forum Software Community Forums UBB.threads 7 Installation and Upgrade Support ubb.threads 7.7.3 install error on create tables

I'm trying to get ubb.threads 7.7.3 installed so I can import a ubb.classic 6.7.3 forum. when I get to the step where you click 'create tables' rather than creating an admin user, it throws the following error:

We Encountered A Problem
Script:
Line:
SQL Error: Specified key was too long; max key length is 1000 bytes
SQL Error: 1071

Query:
create table ubbt_REGISTRATION_FIELDS (
REGISTRATION_FIELD varchar(255) not null primary key,
REGISTRATION_SHOW_FIELD tinyint(1),
REGISTRATION_REQUIRE_FIELD tinyint(1)
) ENGINE=MyISAM


any ideas on how to fix this?

I'm running php 7.2 on this server with mariadb 10.1

thanks!