Hello! The problem is that concrete5 defines plenty of allowed file extensions but not xlsx unfortunately. To add your own extensions, follow these steps:

1. Open concrete/config/app.php and copy the whole line starting with


2. Paste that line into your config/site.php and replace "Config::getOrDefine" with "define".

3. Add ";*.xlsx" (without quotes) to the end of the long extension list, and other extensions you would like to use of course.

The unfortunate side effect of this is that when the app.php file is updated with more extensions, you'll have to copy them to your site.php config file for each update. Not much to do though until the extensions you need is included in app.php.

Good luck, let me know if you have any questions about this!

/Andreas

I don't understand a word of this, but thanks anyway ;)