Using www subdomain causes 404 error - apache

Question

I'm using Apache HTTPD in front of Apache Tomcat with the following virtual host:
$ cat /etc/apache2/sites-enabled/onlinetaskboarddotcom
<VirtualHost *:80>
ServerAdmin comented#out.com
ServerName www.onlinetaskboard.com
ServerAlias onlinetaskboard.com
DocumentRoot /home/ubuntu/www/apache/onlinetaskboarddotcom
ProxyPass / http://www.onlinetaskboard.com:8080/
ProxyPassReverse / http://www.onlinetaskboard.com:8080/
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /home/ubuntu/www/apache/onlinetaskboarddotcom/>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
</Directory>
ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
<Directory "/usr/lib/cgi-bin">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>
The URLs without www subdomain like onlinetaskboard.com/login and onlinetaskboard.com/someOtherValidPage work fine, however once I include the www subdomain like www.onlinetaskboard.com, then I get a 404 error in some browsers like Chrome.
Here are the request/response headers which I observed in Chrome.
With www subdomain:
Request:
Request URL:http://www.onlinetaskboard.com/
Request Method:GET
Status Code:404 Not Found
Request headers:
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
Cookie:JSESSIONID=DE44F60835D23E6AB3CC2A2E8B9D6279
Host:www.onlinetaskboard.com
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/28.0.1500.71 Chrome/28.0.1500.71 Safari/537.36
Response headers:
Connection:Keep-Alive
Content-Encoding:gzip
Content-Length:377
Content-Type:text/html;charset=ISO-8859-1
Date:Thu, 14 Nov 2013 23:39:24 GMT
Keep-Alive:timeout=5, max=99
Server:Apache-Coyote/1.1
Vary:Accept-Encoding
X-Pad:avoid browser bug
And without the www subdomain:
Request:
Request URL:http://onlinetaskboard.com/
Request Method:GET
Status Code:302 Found
Request Headers:
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Cache-Control:max-age=0
Connection:keep-alive
Cookie:JSESSIONID=36D1DED5A3F7B5E185FE5D5EDD4457FC
Host:onlinetaskboard.com
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/28.0.1500.71 Chrome/28.0.1500.71 Safari/537.36
Response headers:
Connection:Keep-Alive
Content-Length:0
Date:Fri, 15 Nov 2013 00:04:33 GMT
Keep-Alive:timeout=5, max=100
Location:http://onlinetaskboard.com/login
Server:Apache-Coyote/1.1
How is this caused and how can I solve it?