Subversion detected a working copy that needs an explicit upgrade in 'D:\work\HYT_V3\trunk\Hyt.Model'.
While this working copy is not upgraded all files in this working copy will appear as new.
When a working copy is upgraded it can no longer be used by Subversion clients that weren't designed for this (or later) working copy formats.
Further working copy upgrade required warnings are suppressed until after you restart Visual Studio or upgrade a working copy.
解决方法非常简单，右键点击解决方案，点击 “upgrade working copy”即可