open your GMail mailbox then open Google Contact
in Google Contact, in the left menu, click on "All contacts
move your mouse over one of the contacts, a check box appears on the left, check this box
Once the box is checked, a menu appears at the top of the page, click on it, and click on "Select all".
the top menu is still visible, to the right, click on the "Group" icon
tick the "SimpleCRM" group
Once done, you can now start synchronization with Google Contact (see http://www.simple-crm-support.com/2014/01/comment-synchronisez-simple-crm-avec-un.html)