warning: preg_replace() [function.preg-replace]: Unknown modifier '''

I had the same error but uninstalling and reinstalling the module did not remove it. As it is, this module does not work after following the simple installation instructions:

• Install the popup_filter module
• Insert [popup] tags in content, and set the input format to "Popup filter" (I used the same popup insert as pinkradical in the previous comment)

I have ruled out the Theme as I have used both Garland and a sub-theme of Zen.

The suspect line of code is this one:
$inner = preg_replace('/\Q'.$result[0].'\E/', '', $inner, 1);

I also installed jQuery 6.x-1.1 for this module but there is no documentation saying if this is necessary in the 6.x branch. If it is a dependency of the Popups Filter module it should be added to the popup_filter.info file with dependencies[] = jquery_update

I've added the dependency in the latest release (6.x-2.3)

I installed Popup filter 6.x-2.3 and jQuery 6.x-1.1 but I was experiencing the same problem as originally described by pinkradical.

I was getting the error:
warning: preg_replace() [function.preg-replace]: Unknown modifier ''' in /.../modules/popup_filter/popup_filter.module on line 464.

When I added this basic popup to a block:
[popup text='Yay this is the popup text!' effect=fade title='TEST POPUP TEXT' link='/']<br /><br />

The problem I discovered was with link='/' in the popup input. It seems that the example does not work well because it was not escaping the / (special character).

If others also get this problem with this example, I think this should be changed/updated in the documentation.

UPDATE: I forgot to mention that I think this module is really amazing and adds a much more effective UI experience for my users. Keep up the excellent work.

Thanks man, good to know it's making a difference.

Here's a patch to fix the attribute parsing of the '/' character

And here's the patch for 5.23

Fixed in v3