It looks like a regular user does not have access to the required configuration directory... try entering the command like this and specifying the -dir location.
./emcli setup -url=https://nsn175-105.us.oracle.com:7803/em -username=MYUSERNAME -dir=/directory/for/my/logfiles -trustall
where -dir is the path to a location for the regular user (MYUSERNAME) to write their log files, and -trustall accepts all certificates.
With this command you are specifying where you want your log fils to be placed(i.e in a location that you have access to) and by specifying the -trustall tag, you are specifying the minimum level of security that you want your emcil to communicate with, to the OMS.
Sorry I wasn't able to get back to you. Lots apologies!
The problem we encountered was due to certification. The very first time we make the call using emcli, login as root user. The emcli setup created a certificate and stored on the local machine. When we change user and login as abc, then we call emcli setup. At that point, the certificate created by the root user is used to compare with the certificate generated by the abc user. Thus the error occurs.
Since the very first time we login as a root user, the subsequent logins with root user there is no complain of errors, but there are errors with other users.
What we did to overcome this problem? We removed the certificate created during the emcli setup call. Then login as a abc user. After that all the subsequent call emcli setup (as abc user) worked.