Why can't I change the isolation levels of my connection in MySQL? I am trying to experiment a bit with the isolation level of MySQL in a test environment.
I do the following: 

mysql&gt; set @@session.tx_isolation='READ-UNCOMMITED';
ERROR 1231 (42000): Variable 'tx_isolation' can't be set to the value of 'READ-UNCOMMITED'


This also fails:  

mysql&gt; update information_schema.session_variables set variable_value='READ-UNCOMMITED' where variable_name='TX_ISOLATION';
ERROR 1044 (42000): Access denied for user 'root'@'localhost' to database 'information_schema' 


What am I doing wrong here? I am root. So it should not be a rights issue.
You need to try
SET tx_isolation = 'READ-UNCOMMITTED';

or
SET SESSION tx_isolation = 'READ-UNCOMMITTED';

You could also declare it at the start of the transaction
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

Give it a Try !!!
CAVEAT
Please note that you misspelled READ-UNCOMMITED (Missing T). It should be READ-UNCOMMITTED
You cannot change tx_isolation in the INFORMATION_SCHEMA database because it is an in-memory read-only database.