known problem with updating data/sending mail?

known problem with updating data/sending mail?

In my databaseapplication is some automatic generated fieldcontent (if checkbox is checked, than the value of something is X...so a totalsum of services can be calculated).
When all fiels all completed and the visitor submits it all, the visitor gets an email with a summary of all the data.

At this moment, it sometimes works not properly. The data are updated in the database, but not all the automatic generated fields are correct. And, the email to the visitor isn't send.

I wondererd if the problem was Vista v.s. XP of the visitor, but that didn't seem to be the problem, the problem occurs on both O.S.
Yesterday even one visitor who updated to different records, discovered that he got only ONE e-mail. I can see in the database the other record had been updated.

Is this a known problem? Is there anything I can do to let it work as I intent to?