I'm having exactly the same problem with exactly the same set up.
Here's my .htaccess file...
##
# @version $Id: htaccess.txt 5973 2006-12-11 01:26:33Z robs $
# @package Joomla
# @copyright Copyright (C) 2005 Open Source Matters. All rights reserved.
# @license
www.gnu.org/copyleft/gpl.html GNU/GPL
# Joomla! is Free Software
##
#####################################################
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE
#
# The line just below this section: 'Options +FollowSymLinks' may cause problems
# with some server configurations. It is required for use of mod_rewrite, but may already
# be set by your server administrator in a way that dissallows changing it in
# your .htaccess file. If using it causes your server to error out, comment it out (add # to
# beginning of line), reload your site in your browser and test your sef url's. If they work,
# it has been set by your server administrator and you do not need it set here.
#
# Only use one of the two SEF sections that follow. Lines that can be uncommented
# (and thus used) have only one #. Lines with two #'s should not be uncommented
# In the section that you don't use, all lines should start with #
#
# For Standard SEF, use the standard SEF section. You can comment out
# all of the RewriteCond lines and reduce your server's load if you
# don't have directories in your root named 'component' or 'content'
#
# If you are using a 3rd Party SEF or the Core SEF solution
# uncomment all of the lines in the '3rd Party or Core SEF' section
#
#####################################################
##### SOLVING PROBLEMS WITH COMPONENT URL's that don't work #####
# SPECIAL NOTE FOR SMF USERS WHEN SMF IS INTEGRATED AND BRIDGED
# OR ANY SITUATION WHERE A COMPONENT's URL's AREN't WORKING
#
# In both the 'Standard SEF', and '3rd Party or Core SEF' sections the line:
# RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
# May need to be uncommented. If you are running your Joomla!/Mambo from
# a subdirectory the name of the subdirectory will need to be inserted into this
# line. For example, if your Joomla!/Mambo is in a subdirectory called '/test/',
# change this:
# RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
# to this:
# RewriteCond %{REQUEST_URI} ^(/test/component/option,com) [NC,OR] ##optional - see notes##
#
#####################################################
## Can be commented out if causes errors, see notes above.
Options +FollowSymLinks
#
# mod_rewrite in use
RewriteEngine On
# Uncomment following line if your webserver's URL
# is not directly related to physical file paths.
# Update Your Joomla!/MamboDirectory (just / for root)
RewriteBase /
#I don't know if this is the rigth thing but here goes nothing...
#RewriteBase /home/webadmin/piksmart.com/html/
########## Begin - Joomla! core SEF Section
############# Use this section if using ONLY Joomla! core SEF
## ALL (RewriteCond) lines in this section are only required if you actually
## have directories named 'content' or 'component' on your server
## If you do not have directories with these names, comment them out.
#
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
RewriteCond %{REQUEST_URI} (/|\.htm|\.php|\.html|/[^.]*)$ [NC]
RewriteRule ^(content/|component/) index.php
#
########## End - Joomla! core SEF Section
########## Begin - 3rd Party SEF Section
############# Use this section if you are using a 3rd party (Non Joomla! core) SEF extension - e.g. OpenSEF, 404_SEF, 404SEFx, SEF Advance, etc
#
#RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
#RewriteCond %{REQUEST_URI} (/|\.htm|\.php|\.html|/[^.]*)$ [NC]
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteRule (.*) index.php
#
########## End - 3rd Party SEF Section
########## Begin - Rewrite rules to block out some common exploits
## If you experience problems on your site block out the operations listed below
## This attempts to block the most common type of exploit `attempts` to Joomla!
#
# Block out any script trying to set a mosConfig value through the URL
RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR]
# Block out any script trying to base64_encode crap to send via URL
RewriteCond %{QUERY_STRING} base64_encode.*\(.*\) [OR]
# Block out any script that includes a <script> tag in URL
RewriteCond %{QUERY_STRING} (\<|%3C).*script.*(\>|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Send all blocked request to homepage with 403 Forbidden error!
RewriteRule ^(.*)$ index.php [F,L]
#
########## End - Rewrite rules to block out some common exploits
