There are certain forms that will render your tax return ineligible to e-file. Please see this for more information: When a tax return can't be e-filed no matter what you do.
Also, depending on which forms you are required to file they may not be available for release in order to complete the e-filing process. Please see the links below for more information about your specific federal and state form status and availability:
Click here for: State
Click here for: IRS/Federal Forms