Problem saving Trigger

[Mike Brett]

I'd appreciate guidance please.

Context is 5.1.24-Community on a remote Windows server (Windows NT MDCRWEB 5.2 build 3790 (Windows Server 2003 Web Edition Service Pack 2) i586).

I've created this trigger in Navicat, my UI of choice:-

CREATE TRIGGER `WhenClosed` BEFORE INSERT ON `n_il` FOR EACH ROW BEGIN
IF NEW.WhenClosed = 'null' THEN
SET NEW.WhenClosed = NULL;
END IF;
END;

and whenever I try to save it (even as root), I get this error message:
1142 - TRIGGER command denied to user 'root'@<<...IPaddress...>> for table `n_il`

If I look at the global privileges set for 'root'@'%', they includes Triggers. I'm obviously missing a trick here, but I can't see what the problem might be!

Thank you.