E-File and Alien Number

[donotspam]

I was trying to do e-file for I-539 extension and on the first page it asks for an Alien number and won't let me go to the next until I fill in a valid A number.

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WARNING: It is suggested that you provide the Alien Number. Failure to do so may result in your application or petition being delayed or denied.
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I'm filling this for my parents and they obviously do not have an A number. I was going to send in paper form, but thought this might be easier.

Thanks.

[donotspam]

anyone?