Also will not be able to Edit any existing Nintex List Form. The Nintex Form designer will display an empty page on the designer without any controls on the side Tool box.
"unable to get property 'FormLayouts' of undefined or null reference"
Check the SharePoint server is not out of space. As the disk space is needed for the log files to be appended to.
The fix is to free up some space and/Or move the log files to a new drive.