"Based on the information you've submitted, your forms of income are considered "exempt from tax."
Due to this, the IRS will not be able to process your return electronically because all the fields will contain '0' values.
The system is prompting you with an error because you may not have a filing requirement.
However, there are various reasons you may still want to file your return. Such as having income tax withheld or making estimated tax payments. Please see IRS publication 501 for more information on Who Should File
Our system and the IRS do not support zero income tax returns to be electronically filed. To use our system, you will need to file a return with at least $1 of earned income. You can enter $1 of earned income on the Additional Income Including Social Security Benefits Page under Other Income.