Multisite error message "Missing or invalid site address"

I am getting this error message “Missing or invalid site address”, when I want to create a new site in multisite. I have created over 40 sites already with no problem, but just recently updated to wordpress version 3.5.2. What could be the problem?

Below is what I have in my .htaccess file.
But I found I am missing wp/ as seen from the WordPress codex Site, the second to the last line as seen below should be like this:

RewriteRule ^(.*\.php)$ wp/$1 [L]

Instead I have in my .htaccess file below as:

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]

# END WordPress

Question 1: Could that be the cause of the error message?

Question 2: If so, can I add the wp/ without messing up my all site because I had a lot of work put into the site already. I cannot start all over again. Please help.