EDIT: RESOLVED! solution: all I did was to restart PC (not sure if this helped too), but then i logged id via console again, typed p4 client, it opened the cfg file, i closed it and then I also had to type: p4 set P4CONFIG="C:\workspace_directory\p4config.txt", now it's working.
original issue: I'm trying to set up my first assembla project with perforce. "p4 info" is Ok, but I cannot run client without the error message. I already set up my connection settings into config file, if I type "p4info". Results:
Client name: my_name
Client host: my_host
Client unknown.
...the others seem to be fine
--name and host are fine, but I seem to need set up my client root workspace directory, but I was unable to find the way how to do it.