In cases where the program is reporting that the license is already used and you have installed it on one computer only, please make sure you have installed inPixio Photo Studio software with the Administrator account, then allow standard users to utilize the software with full control permission.
Keep in mind that Windows is a multi-user system and even though you are the only person who uses the computer that doesn’t mean the user account has administrative privileges granted.
As per inPixio EULA (End User License Agreement), the provided license is a single-user license. In case you need to install the program on another computer, please remove it from the control panel program’s list while the computer is connected to the Internet then use the same license to install it on another computer.