Right clicking any MSSQL Server table gives error 300 VIEW STATE

This mainly occurs when you are using SQL Managment Studio version 2012 or 2008 or earlier than the one on the server.

We have upgraded all servers to SQL Server 2014 hence kindly ensure you are using SQL Server Management Studio 2014:

Here's just SQL Server 2014 Management Studio
- SQL Management Studio x64
- SQL Management Studio x86

This should resolve your error and allow you to edit and select tables again.