Are you signing the TurboTax Account you used with the first download?
The TurboTax user license allows one user to install copies of TurboTax on up to five computers that the user owns. You can prepare multiple returns, including returns for other people. The license does not allow one copy to be shared among different people. You are required to log into your TurboTax online account when you install the program for the first time. This locks one particular copy of the program and one license code to one user account.