Because we had some trouble with Visual Source Safe in combination with Visual Studio .NET 2003.
We use ver 6.0d with VS.net 2003, and we have had some problems as well. Most of opur troubles seem to stem from the facts of the way we choose to use the product. In that if we are NOT carefull when we go to work on something we may inadvertantly lose some code. The problem seems to arise when we have two or more folks working on an item in close proximity to each other time wise. If one person does not make sure they do a full get latest version, and goes on to do some things. they might inadvertantly overwrite someone elses work on checkin. THis is clear pilot error an audit trail will exist to facilitate identification of the correct person so that they may get their flogging.
Another problem that we have had is one of connectedness. If you are out of the office and say open up the IDE, VSS will allow you to operate disconnected. The problem is that it won't automatically reconnect when we go back to the office. THus we may be developing some other things for quite some time before we notice that we are operating in disconnected mode. This seems to be its largest fault.