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output handler can not be used after 'URL Rewriter'
June 2, 2007
2:40 pm


 first of all thanks for such an awesome plugin. I love it.

Now the problem. Everything seems to run fine except that an  error message is being displayed when using Firefox on a Mac and also when using Windows. Safari on the other hand seems to ignore or not display that particular error message and apart from it being displayed the site runs smoothly.

I have modified the styling and default set a bit. I removed the first line of "My Fieldset" and added a captcha at the end instead.

Here is the complete error message:

[code]Warning: ob_start() [ref.outcontrol]: output handler 'ob_gzhandler' cannot be used after 'URL-Rewriter' in /home/ ... /wp-includes/functions.php on line 419[/code] 

Here a short run down of the software and plugins in use:

- OS Mac (10.4.9) Firefox (v2.0.0.4)

- @ 

- Wordpress v2.2

- cforms v4.8

- installed and running plugins:  AJAX comments, Akismet, FeedStats, Google Sitemaps, wp-cache and WP lightbox 2.

I would appreciate some help a lot. Thanks in advance and cheers,


June 2, 2007
6:09 pm
Munich, Germany
Forum Posts: 6400
Member Since:
March 6, 2005

Thanks for the detailed info Daniel, can you on top share the URL so I can see the error msg myself?

Also, it may be that there is a conflict regarding PHP sessions with another plugin, try turning off the others one by one to see which cforms has trouble with (if at all).


June 3, 2007
7:07 pm


 as mentioned above the URL in question would be

 I haven't gone through all the plugins yet but another thing that I noticed was that the first time the page is being loaded the error message is being displayed but as soon as you reload the page it won't be shown again…



June 3, 2007
7:42 pm
Munich, Germany
Forum Posts: 6400
Member Since:
March 6, 2005

It seems that indeed there is a conflict in session management. I suspect that there is another plugin that also uses sessions…

Although it will (possibly) break  the captcha feature, you try to temporarily comment out the sessions call in cforms.php, line ~52:

//need this for captchas
June 3, 2007
7:48 pm
Munich, Germany
Forum Posts: 6400
Member Since:
March 6, 2005

A bit of googling brought this to light.

Try unchecking 'WordPress should compress articles (gzip) if browsers ask for them' under Options/Reading

Maybe that could fix it?

June 4, 2007
2:07 pm

Cool, thanks a lot it works a treat. I'll be definitely recommending your plugin and the kind and fast support.


August 19, 2007
3:42 pm

I faced the same problem, which after looking into the code I could track back to cForms. The problem occurs only with activated gzip-compression. In that case cForms opens a session (session_start();) before Wordpress started the output buffering (ob_start("ob_gzhandler");). So please could you think of moving the creation of the session to a later phase? I really liked to have gzip-compression on.

I tried different hooks, finally this one should work:

### need this for captchas
add_action('template_redirect', 'start_cforms_session');
function start_cforms_session() {


In my tests this code seemed to work well with gzip-compression on.

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