If there is an error that prevents your tax extension from being successfully e-filed, it will return as "rejected". If the cause for this is one that can be corrected, you may be given an opportunity to resubmit it. If the cause for rejection cannot be corrected, you will need to print and mail in your extension.
It was rejected and it is now past April 15th?
When an extension is received before the filing deadline (usually April 15th) but rejected on or after that date, the IRS provides a window, typically five days, in which tax payers may fix issues and correct errors with their transmissions in order to e-file again. Once this date has passed the filer must proceed with a paper return.