Each instance of turbotax (serial number) can only e-file 5 returns. That's an IRS rule. You said you were using your friend's computer? You have three options.
1. Buy your own copy of the program, install on your own computer, register with your own e-mail address. You should be able to e-file from there.
2. Prepare your return using Turbotax Online (register an account under your own name and e-mail address), pay a separate fee unless you qualify to file for free, and e-file.
3. Print your return from your friend's computer and mail it to the IRS for no additional cost (except stamps).
