I am also getting this error (see below with the traceback) which is being thrown when the main login form is being displayed.
Strict standards: Only variables should be assigned by reference in /path/to/wordpress/repo/wp-content/plugins/theme-my-login/modules/custom-redirection/custom-redirection.php on line 92
Call Stack
# Time Memory Function Location
1 0.0010 241176 {main}( ) ../index.php:0
2 0.0015 244536 require( '/path/to/wordpress/repo/wp-blog-header.php' ) ../index.php:17
3 0.3493 33468440 require_once( '/path/to/wordpress/repo/wp-includes/template-loader.php' ) ../wp-blog-header.php:16
4 0.3591 33490448 include( '/path/to/wordpress/repo/wp-content/themes/my-theme/page-login.php' ) ../template-loader.php:74
5 0.4631 34793200 the_content( ) ../page-login.php:26
6 0.4632 34793840 apply_filters( ) ../post-template.php:211
7 0.4640 34796224 call_user_func_array ( ) ../plugin.php:192
8 0.4640 34796256 do_shortcode( ) ../plugin.php:192
9 0.4640 34797304 preg_replace_callback ( ) ../shortcodes.php:201
10 0.4640 34799024 do_shortcode_tag( ) ../shortcodes.php:201
11 0.4641 34799312 call_user_func ( ) ../shortcodes.php:287
12 0.4641 34799400 Theme_My_Login->shortcode( ) ../shortcodes.php:287
13 0.4643 34800240 Theme_My_Login_Template->display( ) ../class-theme-my-login.php:767
14 0.4643 34817616 Theme_My_Login_Template->get_template( ) ../class-theme-my-login-template.php:125
15 0.4655 34836360 include( '/path/to/wordpress/repo/wp-content/plugins/theme-my-login/templates/login-form.php' ) ../class-theme-my-login-template.php:481
16 0.4665 34837816 do_action( ) ../login-form.php:20
17 0.4665 34839312 call_user_func_array ( ) ../plugin.php:470
18 0.4665 34839392 Theme_My_Login_Custom_Redirection->login_form( ) ../plugin.php:470
The error disappears when I remove the ampersand in line 92 in the plugin file/modules/custom-redirection/custom-redirection.php. I changed…
$template =& Theme_My_Login::get_object()->get_active_instance();
to
$template = Theme_My_Login::get_object()->get_active_instance();