Oracle Application - Alert

Every time you use the Alert manager to disable and enable an alert the database trigger associated with the alert got recreated and inside the database trigger there's a submit to a concurrent request to perform the actions associated with the alert.
You can check those concurrent request from the Alert Manager responsibility - Request - View.
If the alert action is not working check the parameters that passed to the concurrent request on the database trigger.

dividing by zero

If you are dividing to a column or sum in your select statement, and there's a chance that the column or the sum result might be a zero an error is going to occur on your select statement; to prevent the error and get a null result you can do the following

select sum(x)/sum(y) from dual; ----- result an error if sum(y) is zero

select sum(x)/decode (sum(y),0,null,sum(y)) from dual --- result is null if sum(y) is zero.

By using the decode, in case of zero the null is going to replace the zero or otherwise take the sum. dividing by null is null.