Recently Facebook has tightened up their screws on its security, so it’s more secure and deals bad acts very strictly. As a part of this Facebook is monitoring user actions in their profile, they do check who all we try to connect, who all do we send request and if they feel that you have some suspicious intensions they blocks your further requests.But sad thing is Facebook is becoming popular day by day and many users are joining, so some of you friends or group of friends might have joined recently and you might have your request to all of them. But if they did not approve for some reason it may end up in this “Do you know this user personally? To prevent misuse of Facebook, this request can’t be sent. To learn more, please visit the Help Center”.
Well I have also faced this but I found out what could be real reason in my case and I hope it may help you also.The main reason behind this is you may be having lot of friends request pending, means the requests you have send to different users, and they have neither approved it nor declined. Those users in that request may be your friend or relative but the sad part is they haven’t added you. So Facebook counts this as you are a stranger to that user. So once your pending count increases Facebook automatically adds your account in that BAD Guy/Gal list, thus prohibiting future request.
So to remove it first Open your Facebook account –> then click on the Account link on the top right side of your Facebook page –> Now you will see a drop down and in that list you need to select Edit Friends –> Now you need to select All connections from the list(left side ,first link) which shows all your friends including your pending requests –> Now you need to remove all those “Pending friends” because this is real cause of the problem –> so find out all those in that list and remove them all (Pending friends request) –> Wait for couple of days ( a week better) and try to send a new friends request.(But don’t over do as you did earlier)
Well this simple method is for all who are legitimate users of Facebook and if you have other intensions it will not work for you. Never send many friends requests to unknown persons. Nor try to send more and more requests at a time.
Also to add on this has worked for me but don’t know it will for you or not.