This looks like the columns being searched are int vs char.

ubbt_FORUMS FORUM_ID is int(9)
ubbt_FORUM_PERMISSIONS FORUM_ID is varchar(100)

If you turn off SQL strict mode, the error you have now should turn into just a warning, and you will be able to proceed.

But i believe this may be easily fixed at the code level by just adding single quotes around the string.

Give this a shot

FIND IN admin/dodeleteforum.php AROUND LINE 35
		delete from {$config['TABLE_PREFIX']}FORUM_PERMISSIONS
		where FORUM_ID = ?

		delete from {$config['TABLE_PREFIX']}FORUM_PERMISSIONS
		where FORUM_ID = '?'