Notice: Undefined index: #validate in logintoboggan_prevent_form_alter()

this is conflict with logintoboggan-login-block-type changes.
you need to wrap some lines like this in logintoboggan_prevent.module

case 'user_login_block':
      // add us right before user_login_authenticate_validate
	  if (isset($form['#validate'])) {
	  	$key = array_search('user_login_authenticate_validate', $form['#validate']);
      // cutoff including searched function
      $chop = array_splice($form['#validate'], $key);
      // append our validation
      $form['#validate'][] = 'logintoboggan_prevent_authenticate_validate';
      // append previously chopped functions
      $form['#validate'] = array_merge($form['#validate'], $chop);
	  }
      break;

I had the same problem.
#1 solved it.
Thank you.