You may be encountering a problem adding on a contact manually into your account?
1. Have you inserted both a First Name and Last Name into those fields, which are mandatory?
2. If you are inserting an email address, is the address valid with no spaces or invalid characters?
3. If the email address is valid but the contact is still not adding then it is possible that the email address is already in your account. Email address is a unique identifier and within your account you can only have each unique email address for contacts in your account once. To check if that email address is already in go to Contacts and search for the email by selecting Email and pasting the email address in the search box. You also have the advanced search to use if you need to.
If you are still having problems then please raise a support ticket to us and we will look into the matter further.