I personally use

try_files $uri $uri/ /index.php?q=$uri&lifier$args

which normaly works fine however in this situation it really works just for posts, for groups I recieve 404 error.

It is not theme problem because same is going on using the default theme.

Anybody have knowledge about this?

i have a complete guide for establishing nginx and WordPress

http://themesforge.com/featured/high-performance-wordpress-part-3/

hope this can help,

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