Need help with ERROR: OpenSSL::PKey::RSAError: private key needed

Hi,
Im getting the following error with knife user list
ERROR: OpenSSL::PKey::RSAError: private key needed.

i have downloaded the pem files from web GUI. have placed knife and pem
files(downloaded from webGUI).

I’m not able to find pem files at /etc/chef/ in chefserver. please guide
me, are these pem files different from the pem files downloaded from Web GUI

Regards,
Sakhamuri.