adding records

I use a PHP script to add records to my database. It usually works very good, but from time to time it refuses. I enter my data through a data entry form. After I tell it to add the record it normally displays the data to be added shortly and then my data entry form reappears. Frequently however the data stay on screen - in two versions, one below the other - and the data entry form doesnt reappear. Instead I am told that something went wrong and that I should push the back key and alter the data manually. Doing that brings me back to the normal data entry form with my data in it - not twice - everything looks normal. Data entry remains impossible. What is wrong here? Thanks Theo Richel