Unable to complete installation on existing site

I'm trying to install FLEXIcontent version 2.0.2 r1680 on Joomla 2.5.11.
It works perfectly on a new site. However on an existing site with a few articles and categories everything goes well until I get to this message:

Please open and save Configuration. Then REFRESH and this message will disapear .

When I open the configuration and hit save the popup window remains blank forever and if I force close it I still have the same message.
On a new installation after saving the configuration the window refreshes and the message disappears.

I tried to uninstall and reinstall several times, checked my categories, made sure the had a valid parent and so on, checked that my articles had categories. I still can't get past the message.

Any suggestion?
Thanks.
I don't want to lose the content of my site. How can

Hello,
did you try this ?:
I am continuously asked to resave the Global Configuration

Also after installing FLEXIcontent, try this
- clear cache and relogin

Hi,

I did try everything mentioned in the other post.

a) returns error 500 so I tried b) but then I get the global configuration popup to display

Forbidden

You don't have permission to access /administrator/index.php on this server.

Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.


I also checked the database #_extensions is OK and params is of type text.

Unfortunately I cannot change the php version. I may have to migrate my original site to another hosting provider. Bummer.

Hello
please check the apache error logs via visiting cpanel and looking at the "Error log"