I am having issues with Selection using QGIS 2.0.1. Dufour. When I select one point, all of the points get highlighted. Attribute Table dialog shows Errors for all of the attributes. It indicates that Features total:12691, filtered:12691, selected: 1. Has anyone else experienced this issue?
There is a bug in QGIS 2.0.1 when it comes to SQL Server [uniqueidentifier] data type. QGIS 2.0.1 does not know how to handle a column that is defined to be [uniqueidentifier]. It exhibits the behavior described in my question. In my case I had [GlobalId] [uniqueidentifier] which was the primary key as well. Once I removed the [uniqueidentifier] then all was normal.
Your table does not have a primary key.
QGIS must detect a primary key to work.
Make a primary key field in your table and everything should go OK.