I had to uninstall and then download and reinstall Movie Magix pro plus 2021. It now tells me error 24 even though I have the P3 number and email correct. How do I over come this as it says this is registered to another email?
First, assuming that the process you followed to uninstall and reinstall the software was actually successful - you didn't tell us why you followed this route, and it is very easy to actually make the original problem worse by doing so, unfortunately - I would suggest the following to enable you to successfully register and activate the new installation:
Go to your Magix account, log in and go to My products.
Find the listing for your version of MEP and deactivate any and all existing installations that you no longer need.
Go back and try again to register and activate the new installation.
If the new installation is now fully up and running, fine.
If it is not, and either the above procedure failed, or the original problem is still present, you need to look at carefully removing ALL traces of your current installation from your computer. A number of users here, myself included, use Revo Uninstaller (either the free or paid-for Pro version) to ensure everything connected with a prior installation is removed (as part of its Advanced scan it will search for and show you a list of all the files, folders, registry entries etc. that it believes are connected to the original installation) - just ensure you check carefully everything Revo lists there, especially if you have any other Magix programs on your computer. Once it has finished, reboot your computer and retry the reinstall and registration/activation, repeating the three steps I suggested above.