Can't save settings from system console (v.3.0.1)

Just dealt with this right now. In my case the issue was I had nulls in part of the config file.

Specifically, I had to change the Ldap block from:

    "LdapSettings": {
        "Enable": false,
        "LdapServer": null,
        "LdapPort": 389,
        "BaseDN": null,
        "BindUsername": null,
        "BindPassword": null,
        "FirstNameAttribute": null,
        "LastNameAttribute": null,
        "EmailAttribute": null,
        "UsernameAttribute": null,
        "IdAttribute": null,
        "QueryTimeout": 60
}

to this:

    "LdapSettings": {
        "Enable": false,
        "LdapServer": "",
        "LdapPort": 389,
        "ConnectionSecurity": "",
        "BaseDN": "",
        "BindUsername": "",
        "BindPassword": "",
        "UserFilter": "",
        "FirstNameAttribute": "",
        "LastNameAttribute": "",
        "EmailAttribute": "",
        "UsernameAttribute": "",
        "NicknameAttribute": "",
        "IdAttribute": "",
        "SkipCertificateVerification": false,
        "QueryTimeout": 60,
        "LoginFieldName": ""
}

For your profile images, you might want to check what value you have for FileSettings.Directory in your config.json, and the permissions on that folder.