Hi Yvie,
Thank you for your post and we apologize if you are unable to print invoices during a locked period. We are aware of this issue and the developers are already working for a permanent solution. Alternatively, if your file is in the cloud you can print or email the sale from the browser. In Accountright you may disable the lock period temporarily to print or email existing sales.
The lock period can be changed from Set Up > Preferences > Security.
Feel free to write a post if you need further assistance.
Cheers,
Jem