Hi,
There is problem while loading new MSN website usign the Safari browser. Make sure that you have latest version of the Safari installed on your MAC computer.
As a work around you can try to open new MSN website on a different browser and check if you are able to post comments.
Disclaimer: Using Third Party Software, including hardware drivers can cause serious problems that may prevent your computer from booting properly. Microsoft cannot guarantee that any problems resulting from the use of Third Party Software can be solved. Using Third Party Software is at your own risk.
Let us know the status of the issue, we will assist you further.