I am calling the MergeContent method on a TFS workspace (App.Instance.TFSWorspace in my example) as shown below:
bool result = App.Instance.TFSWorkspace.Merg
A couple of potential reasons this may occur:
diffmerge.exe is not in the path of your running program The default external merge tool is diffmerge.exe found in \Microsoft Visual Studio 10.0\Common7\IDE (maybe different based on your version). If this is not in the path of your program it will fail to start the diffmerge process when a conflict occurs
Program does not have a UI shell This can occur if your program is a service or web app. This may not be the case for you but I was not completely sure from the description
Most likely the issues is #1 above. I would check that first.