To solve this issue, please try to remove the content of Temporary Internet Files (open Internet Explorer ->Tools menu -> Internet Options -> Temporary Internet Files section -> Delete Files button -> Delete All Offline Content).

Then, please reboot your computer and try to download the latest installation file of the appropriate edition that you have ordered.

In case you are using some security application for contents filtering (CyberSitter, Content Watch ...) please make sure [www.grisoft.com] [akamai.grisoft.cz] [update.grisoft.cz] [download.grisoft.com]  is set as a trusted one (so files coming from it are not filtered / modified) or try to temporally turn the content filtering application off.

If the problem still persists, it is probably caused by instable Internet connection.  Suggestions to deal with instable Internet connection are listed here.