Hi,
Try running this query and check the results:
select Code, Name,Priority,Active,NextDate,NextTime, LastDate,lasttime from oalt
In my case, the NextDate & NextTime were NULL, meaning it would not trigger, even though it was active.
I messed with the alert set up by changing recipients, frequencies etc until my query populated with a next date, then reset as I wanted it. It is now working fine, but took a wee while