System.Runtime.Serialization.DataContractAttribute' does not contain a definition for 'IsReference

This is indeed not the brightest thing that could happen to your .NET framework installation and the cause of the problem seems to be installing Expression Studio and probably the 2.0 version of Blend. The frustrating part of it all is that when you get this problem there is probably like for me only one solution. You can't reference the Assembly that is in the GAC anymore. You need to pick browse every time you need System.Runtime.Serialization.dll.

I had a look at the file on my private computer where the problems started. the version that is in the GAC for me is an old version from january 2008 but on my work-computer the version is dated 30th of june 2008.

There is no easy way of replacing that january version but this is what I did. I searched for Runtime.Serialization.dll on my troubled computer and just browsed to one of those files from within Visual Studio 2008.

Problem solved, no more System.Runtime.Serialization.DataContractAttribute' does not contain a definition for 'IsReference anymore.

This is something you need to adress at microsoft. No installation should overwrite newer versions of ANY dll please!