Hello All
After upgrading joomla to 3.5 (by ftp uploads) and updating to the latest K2 version (from site backend with joomla update manager) the when i trye to open media manager in frondend and in backend I got the follwing error :

Invalid backend configuration.
Readable volumes not available.

Hello,

Can you try disabling error reporting.
This setting can be found in your site's global configuration menu.

unfortunately after changing error reporting parameter the problem is not solved and it stays the same error.

With "none" or "system default" value I got this message :

Invalid backend configuration.
Readable volumes not available.

with "simple" , "maximum" and "developement" values, I got :

Invalid backend response.
Data is not JSON.

Ok, keep none for error reporting.
This could be related to a couple of causes.

a) Permissions, Please install Admin Tools from www.akeebabackup.com/downloads/admin-tools.html in order to fix your permissions as they should be and then reinstall the extension.

Right permissions on all joomla sites:
755 for folders
644 for files

Admin Tools can fix any read/write "file" permissions on your site, to what they should be. But, if your server's "owner" permissions for files are not properly setup, in other words, if Joomla cannot perform read/write operations via PHP, then it will not work properly.

b) Your hosting provider might be stoping symlinks from functioning.

I'm expring the sam problem and nothin of above have help me? There is now way to uploading images for me at this time in K2? When using "Item image" to upload nothing happens and when using "Brows on server" I get "Data is not Json"

What to do?

Thanks in advance
/Regards Thomas

Can you try disabling error reporting?
This setting is located in your site's global configuration options.

Hi and thanks for the answer. I have disabling error reporting. But it's still the same.
Regards Thomas

Do you still get DATA is not JSON or Invalid backend configuration.
Readable volumes not available.?

Hi, Yes! This is what I get: Invalid backend response.
Data is not JSON.

Regards Thomas

Check this topic also
www.joomlaworks.net/forum/k2-en/28435-resolved-invalid-backend-response-data-is-empty