This is the most comprehensive article about the event of being blocked on this website and I hope you will read this when it happens.
Q: Why does your website block me?
A: I have several automated security measures in place that protect my data and my website's members and reputation. I'm currently doing a better job than for example Marriott, Sony and other (large) companies. I defend my and your data aggressively. This website is under all sorts of attacks on a daily basis and sometimes the defence system causes a so-called false positive.
Q: I am blocked while I download not more than 5 items per day!
A: You downloaded for more than just a few models, did you? ;) The download system has an analyser built in that keeps a virtual eye on all downloads. Yes, of course, you can have more than a few models in your garage, but when the system detects a certain pattern in the downloads, it will raise a flag. Just contact me and I'll help you out where possible.
So, with this out of the way, let's get into this matter once and for all:
Step 1. Do you use a VPN?
If so, good for you. It is good practice to use a VPN since it makes your connection to the internet a lot safer from prying eyes and it anonymizes you so your origin cannot be easily traced. But there is a snag to all this wonderfully encrypted traffic. You are a good person I'm sure and I'm also sure that you don't do evil things on the internet while using this VPN. However, there are other people who are not so nice and use a VPN to stay anonymous while they are doing bad things.
"So how does this affect me?", I hear you ask. Well, a VPN offers a wide choice of gateways through many countries and per country they have a limited amount of IP addresses. And here's the problem. Your router in your home has a unique IP address assigned by the Internet Service Provider. No one else is currently using your current IP address.
A VPN is using SHARED IP addresses. So many people can use the same IP address since traffic gets channelled through this address from your house to the website you are visiting. So if someone using this VPN is using the shared IP address to send out spam, this IP address will be flagged as a source for spam. This gets then put into many spam-prevention databases. If you are the unlucky one that is also using this shared IP address, you run into trouble with accessing and/or registering at websites.
Solution: The last thing you want is to switch off your VPN. So do change to another gateway in your country or change the country altogether. There is a chance that you get a shared IP address that is not flagged and then you can proceed to visit websites. This is not always working and then you need to switch your VPN off, unfortunately. You then need to rely on your antivirus and firewall programs on your computer.
Step 2. You don't use a VPN? Then your assigned IP address may be flagged.
Your Internet Service Provider gives your connection an IP address. This is a unique number which makes it possible to communicate between your computer and any other computer or server on the internet. This IP address is not a permanent one. You "lease" this IP address until it expires and then you get assigned a different IP address.
Now imagine the following scenario: Someone on the internet is an actual spammer or does not have their security in good order. This person's IP address will then be flagged in a number of databases as suspicious. The IP address of this person expires and gets assigned a new one. (possible tainting yet another IP address) Your IP address expires too at some point. If you're then unlucky and get the spammer's IP address, you will then get blocked at various websites for having a suspicious IP address. This is just a fact of internet life. Flags also expire and then the offending IP address is clear again.
Solution: Switch your router off for about 15 minutes. This usually triggers an event at the Internet Service Provider that the IP address is not active and will then be set to expire. When you then switch your router/modem back on, you will get assigned a new IP address which then hopefully is not flagged.
Step 3. Your email address may have been flagged
Many companies, large and small do not have their security up to spec and leak millions upon millions of email addresses to hackers who gladly collect them and sell them off to potential spammers. This means that spam has possibly been sent in your name, by faking the sender address to look like yours for example. Then your email address gets flagged as suspicious. This too usually expires at some point.
Solution: Contact the website owner and ask to be white-listed
Edit: Corrected some grammar and typos