每次打开由TFS源代码管理的项目，.sln的文件都会被自动签出，如果什么都不修改，直接签入，TFS会告诉你什么也没有改变。
上网搜索了一番，找到了一篇文章，用其中的第四种方法解决了这个问题：
4) You can also try below workaround:
Check-out your solution file from source control
Open the solution file in a text editor, like Notepad.
Find a section named "GlobalSection(ExtensibilityGlobals)"
Delete the entire section, including the opening and closing section markers.
-- GlobalSection(ExtensibilityGlobals) = postSolution
-- through
-- EndGlobalSection
Save the solution file in the text editor
Check the solution file back in to source control
Open the solution in Visual Studio