This question has been raised many times in the forum and I was eager to find a solution with NF.

How can you allow the users to submit only once.

I had this working in the InfoPath but did not get any success on Nintex Form (probably messing up a very basic lookup).

Here are the steps to create a form which can be submitted only once by the users.

1. Create a list and add an additional column:

     a. UserName - single line text.

2. Edit the form with Nintex.

3. Add 2 panels on the form. In the first panel add the form fields that you want the user to enter. In the second Panel add the text - "You have already submitted the form once" - bold.

4. Change the configuration of UserName field as below:

This way you are saving the value of the current user in the uppercase. You can hide this field in the form is you want.

5. Add a calculated value control (I called it GetName). Enter the formula as shown below:

     lookup("<ListName>","UserName",toUpper(Current User),"UserName")

     This will lookup the list where you are creating the form. Find if the UserName column has the same value as current User (in uppercase). It will return the value from that column.

6. Lets add rules to the panels now. Add rule to the first panel where all the fields are: greaterThan(length(GetName),0) > Hide. (SO if the lookup returns the value that means you have submitted an item already).

7. Add another rule to second panel where you have the text: lessThanOrEqual(GetName,0) > Hide. (If lookup returns blank, you have not submitted the item).

Save and Publish.

Now when you create item, you should see the form with the fields and would be able to save it. Second time, it should show the panel with the text in bold: "You have already submitted the form once".

Hope it works for you.