(Web part) How to get current logged in user's properties?

Hi,

I'm new to SharePoint development and I'm currently working on developing a web part in My Site. I've been trying to get the logged in user and user properties but haven't succeeded so far.

I've been following the code examples in C# on the MSDN site:
http://msdn.microsoft.com/en-us/library/jj163913.aspx

as well as this one:
http://www.sharepoint2013.me/Blog/Post/114/Get-User-Profiles-and-User-Profile-Properties-in-Sharepoint-Programmatically

I'm not sure why but it seems that an error occurs at the line

            clientContext.ExecuteQuery();

and I haven't found any documentations for this error when troubleshooting.

Any help or suggestions would be very much appreciated!
Thanks!