A connection was successfully established with the server, but then an error occurred during the pre-login handshake

Solution

1) Clean your VS.Net Solution

2) Rebuild Project.

3) Reset IIS

4) Run the project again.

Basically that solved my problem, but in my case i was not getting this error and suddenly my local environment starts giving me above error, so may be that trick work for me.

• Save your work,
  
• Close Visual Studio, then
  
• Re-open your project

This worked for me.

Running the following command worked for me:

netsh Winsock reset

Seen at https://serverfault.com/a/487139/250527