Problem:
because of a protocol error, this session will be disconnected. Please try connecting to the remote computer again
Solution:
The most common reason why this is happening is because you are using a custom VISUAL STYLE with your computer. Set the visual style back to LUNA on XP or CLASSIC and see if the error occurs again. Most likely it will not. Not all visual styles produce this error, but if you want a custom visual style on the remote computer then you will have to find a compatible visual style that works with RDP via trial and error.
Another solution would be to set the RDP client to NOT use the visual styles by unchecking the box that says THEMES (see pic below):
Original Link :http://computerboom.blogspot.com/2008/08/solution-because-of-protocol-error-this.html
Hope this will help!,
Amith Prasanna