Problem Statement
At the time of copy the transaction screen associated with customer display its showing

Error “Cannot save CustomerDisplayTransactionLayout. CustomerDisplayTransactionLayout not valid. Error- Code/Id cannot be left blank”
Symptoms
NA
Resolution/Work Around
We can copy transaction display screen through below steps
1. Click on Copy at Customer display transaction search
2. Click on Customization
3. Drag the column: layoutControlItem1 and keep it at main layout.
4. Now Code & Description field is visible to enter the value.
5. Click on Ok to save the screen.
Please find the below screenshot.