Hi dottie,
You'll need to dive into the screen designer by editing the screen and take a look at your customized actions to find the problem. What triggers the job number to be generated? Is it a Save button? You'll find the actions that create the job number in the button that triggers it. You should find a Basic Math Calculation action that will first create an action result. You should then find a Update Field in Table action which places the math calculation action result into your job number field.
Check with whoever customized these actions to see if they are still set up correctly. They may be referencing a field that doesn't exist in the new account and therefore would need some tweaking. You could also compare the actions in your two accounts to see how they are different. I included a couple of screenshots of what the Basic Math Calclulation and the Update Field in Table actions generally would look like. It most likely will look different in your case depending on how this customization works on your account. Update Field: should reference your job number field, in my case I had a field called PlusOneNumber.
Jason
