I have ssu v3.7.1 installed on zc 1.3.8a and my htaccess is:

#### BOF SSU
Options +FollowSymLinks -MultiViews
RewriteEngine On

RewriteBase /

# Deny access from .htaccess
RewriteRule ^\.htaccess$ - [F]

RewriteCond %{SCRIPT_FILENAME} !-f
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^(.*) index.php?/$1 [E=VAR1:$1,QSA,L]
#### EOF SSU

and I double checked with my hosting company, mod rewrite is on.

Anything else that I can check?

and yes, I have module manager installed and working.