PDOException: SQLState 22001

When doing an import into Drupal 7.23 from vBulletin 3.84 or 4.05 the test setup works fine. I get the message about truncated title at 64 character (which I thought was fixed in this dev version), ignoring that I click to import and a couple seconds later this error stops the process.

An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /batch?id=45&op=do StatusText: error ResponseText: PDOException: SQLSTATE[22001]: String data, right truncated: 1406 Data too long for column 'signature' at row 51: INSERT INTO {users} (pass, mail, created, access, login, signature, name, status, timezone, uid, picture) SELECT u.password AS password, u.email AS email, u.joindate AS joindate, u.lastactivity AS lastactivity, u.lastvisit AS lastvisit, COALESCE(utf.signature, '') AS signature, SUBSTRING(username FROM 1 FOR 60) AS name, 1 AS status, timezoneoffset*60*60 AS timezone, u.userid+:add_to_ids AS uid, IF(ca.userid IS NULL, 0, ca.userid+:pictures_add_to_ids) AS picture FROM {testvb.user} u LEFT OUTER JOIN {users} du ON u.username = du.name LEFT OUTER JOIN {testvb.customavatar} ca ON u.userid = ca.userid LEFT OUTER JOIN {testvb.usertextfield} utf ON u.userid = utf.userid WHERE (du.name IS NULL ) LIMIT 100000 OFFSET 0; Array ( [:add_to_ids] => 1000000 [:pictures_add_to_ids] => 60000000 ) in vbimportapi_import() (line 1015 of /var/www/vhosts/website/ver6/sites/all/modules/vbtodrupal/vbimportapi.module).

When I click to view the error the message I get is:
An error occurred while processing vbimportapi_import with arguments: Array ( [0] => user [1] => 100000 [2] => vbtodrupal [3] => vbtodrupal )

I've tried this with my final module install as well as with a bare minimum install, same error.