When you try to add new connections in Linkedin and it suddenly starts to ask to enter the email of the people you’re trying to connect to, this is usually caused by your previous failed attempts to expand you network.
Probably too many responded that they don’t know you, yeah some douchbags just can’t grasp the idea of social networking. Linkedin itself want’s you to add only those contacts who you know in person. How Linkedin is supposed to help building relationships for a successful career in this case is a mystery. Anyway, sooner or later you’ll get the chance to plead guilty and ask for remorse in the form of a yellow rectangle just before the email prompt. Accept it, and the restriction will be lifted. You can now add new connections without knowing their emails.
Please note: You are now required to enter an email address to send invitations from this page because several recipients of your invitations indicated they don't know you. This safeguard is in place to prevent users from receiving unwanted invitations from people they don''t know. You can remove the restriction at any time by indicating that you understand this policy Invitation Restriction Your account has been restricted because a significant number of LinkedIn users whom you have invited to your network have indicated that they don't know you. Use of LinkedIn is subject to the terms of our User Agreement, which you have violated. An example of the violation includes breach of Section 11, LinkedIn User DOs & DON'Ts. "As a condition to access LinkedIn, you agree to this User Agreement and to strictly observe the following DOs and DON'Ts: Don't - Invite people with whom you have no prior relationship to join your network." By selecting the checkbox and clicking "OK" you Agree you will comply with all the terms of the User Agreement. If you violate the agreement, you acknowledge that your account may remain permanently restricted or be closed by LinkedIn.