Cannot resolve error 304 in my magento Shop

Hello,

I recently switched from Apache to NGINX. So far I like this Server. Pretty fast and easy to config. Now I am experiencing problems using a Magento Shop running on NGINX. Installation works fine but when it comes to working in the backend I am having dozens of 304 erros not showing images, js and css which makes the backend unusable.

I am running NGINX on a preconfigured PLESK and added following directives:

if_modified_since off;
proxy_set_header If-None-Match "";
add_header Last-Modified "";

to webserver settings for my domain. I also tried to add these directives to the nginx.conf.

Neither works for me. The browsers (Firefox, Chrome) will always return 304 errors. Sometimes I see some more images and tables when I refresh the pages or empty the cache. I also emptied the browser caches several times.

I am working on this problem for days now and I cannot figure out a solution.

I really tried my best googling and reading articles but all did not work.

Can anybody point me in the right direction?

Thanks

Danska