The site is saying my control no. Box D must be more then one number or letter. However my control no. is only one number.

[AndreaC1 · Accepted solution]

You can just put in any combination of numbers in this specific format 5 digits, space, 5 digits (for example, 12345 67890). 

That is just a number that the payroll team uses to identify your W-2 for their system purposes. Sometimes it may be blank since that is optional to them.

You can find more details on Box D and the Control Number here https://ttlc.intuit.com/questions/2669624