Friends request blocked - not sure why, suggestions welcome

I only send friendship requests to people that:
1 - appear in my "People you might know" section on top right of my wall (i.e. FB itself is suggesting me....)
2 - share with me "at least" one common interest, more often 2-3
3 - have "at least" 4-6 friends in common with me
I have been sending some 12-15/day requests in the last week and I always attach a message to explain who I am, why I send the request and for what purpose.
However, last Sunday my request permission have been blocked for 4 days......
Not only I can't send new requests, I can't even reply to friendship request I AM receiveing (which I find weird, to put it politely....).
Is this a typical behavior from FB? What are the rules and limits about this issue?
I thought that FB members have the option in their settings to prevent unwanted requests and if they haven't done so, I suppose it's because they are prone for considering new friendships ALSO from people they don't know actually.
I.E. if you allow people to send you a request, why do you mark some of them as spammer?

I'll be very grateful for any explanation about this issue.
Fabio


[Moved to Friend and Requests]

Hi Fabio, It's very likely that many people receiving your invitations marked you as spammer.

My suggestionto you is
Do not add people you dont actually know.
Even if you are just being friendly, It is considered as intrusive for some people.
Keep an Email conversation with them first.
Tell them why do you want to add them.