Like first, we assure you that Magiesta is not harmful or virus-containing software. Magiesta does exactly what is intended for.
The most common reason is that antivirus reports magiesta.com as false positive site; go to your antivirus settings and exclude magiesta.com from list of suspicious sites (or add it to the filter list). This is a fairly usual situation that normal site is for some unknown reason blocked.
Secondly, we are not sure what could cause this problem, but it is indicative that most reported problems comes from specific address, in other words ISP (Internet Service Providers). Furthermore, we were unable to reply on email messages received from all mentioned users because of some high restrictions on their ISPs / mail servers. Please contact your ISP or mail provider in order to get reliable information about what's happening, they should give you information about all the sites that you want to access - whether they are restricted (and why) or not.
Also, keep in mind that it is possible at any time that actually your computer is the one infected with virus that presents itself as a antivirus.