When already logged into the Management Console you will be unable to add packages via MSI and will be presented with a '403 forbidden' message. This will apply regardless of your server permissions.
You may be also find that logging on to the server from the console only succeeds using a 'localhost' connection, but using the FQDN or server name may also result in a 403 message.
The error in IIS logs will be 403.502 messages as below:
2013-04-26 18:43:1010.1.240.19 POST /ManagementServer/DataAccess/Alerts.asmx - 80 - Mozilla/4.0+(compatible;+MSIE+6.0;+MS+Web+Services+Client+Protocol+2.0.50727.5466)403 502 0 31
The module supports return status codes 403, 404 or closing the connection
It will depend on the settings for this extension, but to avoid potentially receiving this error (amongst others you can also set) you can remove this setting or amend as applicable.