I have a workflow rule in place that updates ReminderDateTime when from another custom DateTime field which is a formula field on the same object. But eventually when i tried complete a task, i am encountering this error "The formula in the "TaskReminderSet" rule or process is invalid due to the following:
Computed an invalid date, such as February 29th on a non-leap year. Please contact your administrator; formula fields can cause such errors.
Elaboration: Added two field to the Activity Custom Fields as "Time__c" as picklist value where users will be able to select time from dropdown like 9:00 or 9:30 etc.. and another DateTime custom formula field ReminderDateTime and the formula in that is
DATETIMEVALUE(TEXT(YEAR( ActivityDate ))+"-" +TEXT(MONTH(ActivityDate ))+"-" +TEXT(DAY(ActivityDate ))+" "+TEXT( Time__c )+":00")+300/1440
So when the users save the task with DueDate and Time selected, the custom ReminderDateTime field will be save using the formula while my workflow rule will update the Reminder section under tasks as Reminder to True and Date Time for that from the custom ReminderDateTime value.