System.IO.IOException: unable to read data from transport connection: connection was closed at ReadKey

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C#

Hello.
I have been trying to do posts on some sites, which works fine on most, but there are few exceptions.
If I use httpprotocol1.0 it works fine, but then again some pages cant be loaded completely and the last html source is missing.
If I use httpprotocol 1.1 it also works good on most sites, but there I do get exceptions (on the same sites that gave me problem on 1.0 as well).
My exception is,
System.IO.IOException: unable to read data from transport connection: connection was closed at ReadKey

Have tried several of different ways to load the page, but it just wont work. I sniffed my http requests and responds, but they are the exact same for the working and non-working.

What can occur this error?
Hope someone can help, I have stocked for many hours and days with this problem.

Thanks