Begin End - Not Executed

hello, I have a big problem with a script.. some instructions seems to be not executed. I don't understand. If I execute line perline it's ok - but the entire block no.
Explain me and find the solution:

IF NOT EXISTS ( SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'ACS_ACL'
AND COLUMN_NAME = 'ZoneUId' )
BEGIN

ALTER TABLE dbo.ACS_ACL ADD ZoneUId T_UID;

UPDATE dbo.ACS_ACL SET ZoneUId = '1' WHERE ZoneUId IS NULL;


print 'end of script'

END



result:

Msg 207, Level 16, State 1, Line 9
Invalid column name 'ZoneUId'.

the error is on line:
UPDATE dbo.ACS_ACL SET ZoneUId = '000000001' WHERE ZoneUId IS NULL;

how is is possible because the preceding line is

ALTER TABLE dbo.ACS_ACL ADD ZoneUId T_UID;