There is an inbuilt download limit of 10 downloads per product to prevent download links being stolen from people who have purchased the product and posted online. Usually this is enough downloads for you to be able to get the product you have purchased and load it onto your device (and reload it a few times if you upgrade your device etc).
The best way to avoid reaching this limit is to ensure that you are saving the files to your device after clicking the download link in your order confirmation email.
If you’ve reached this limit and need it reset, I am happy to do this for you (at no cost) – simply complete the form at the bottom of the page and I will have it fixed within 24-48 hours.