Cannot start TRANSACTION

[Haseeb Iqbal]

i am using MYSQL 5.0.3 beta-standard.

i wanted to run a few commands and rollback if any of the commands failed. but i noticed that if i tried to rollback. it just wouldnt do. i was using php so thought maybe php is having problems. i created a sql script and tried to run the commands and rollback but with no luck. then i tried this
=====================================
START TRANSACTION;
SELECT @@autocommit AS AutoCommit;
ROLLBACK;
====================================
AutoCommit always returns 1. which means Autocommit is turned on, then i tried to chnage the above to SET autocommit=1; but after i executed the command i sartted getting

Error: 1192 SQLSTATE: HY000 (ER_LOCK_OR_ACTIVE_TRANSACTION)

Message: Can't execute the given command because you have active locked tables or an active transaction
i was using this script
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SET AUTOCOMMIT=0;
SELECT @@autocommit AS AutoCommit;
ROLLBACK;
====================================

what am i doing wrong and what can i do tto fix this issue

Thanks