1st check the permissions and ownership values on the "/home/$username" and "/home/$username/public_html" directories to ensure they match what's used for other accounts on the server.
2nd Browse to "WHM >> Tweak Settings" under the "Security" tab and let us know if "Enable File Protect" is enabled. If not, try enabling it, then disabling it again to reset file permissions on the public_html directory to default. If it is enabled, try running the following command to correct the permissions:
/usr/local/cpanel/scripts/enablefileprotect