File manager hangs 20 s. when opening folder or gaining focus

Hello,

My file manager hangs for about 20 seconds almost every
time I open a new folder or I give focus to a previously
open one.
Then, suddenly, everything gets right and I can work
normally.

My network administrator had look for DNS conflicts but it
seems not to be the source of my problem.
I've also try to set the file managers windows working in
separated processes.

Thanks a lot for any help.