If anything went wrong during the download of your software, you might see a checksum error.
To solve this error you need to clear the cached packages on the disk. To do so follow these steps.
First open the settings tab by clicking the cog wheel in the top right corner.
You will now see the folder on your computer where all the packages are stored. Remove the package that is causing the error. (or you should be able to remove them all, the will be download again when needed.)
Now follow the normal install procedure by clicking install in the main tab of the License Manager.