Ever get: "Warning MSB3061: Unable to delete file " message towrds the end of a build, eg:

 

  BUILDREL: BUILDMSG: Cleaning up "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release"
C:\WINCE800\public\common\oak\misc\buildrel.proj(495,5): warning MSB3061: Unable to delete file "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release\proxydriver.dll". The process cannot access the file 'C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release\proxydriver.dll' because it is being used by another process. {log="C:\WINCE800\build.log(40826)"}
C:\WINCE800\public\common\oak\misc\buildrel.proj(501,5): error : Error cleaning up flat release directory "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release".  Unable to delete the following file(s) "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release\proxydriver.dll".  Please make sure there are no other processes using these file(s) and try again. {log="C:\WINCE800\build.log(40858)"}
  C:\WINCE800\public\common\oak\misc\buildrel.proj(495,5): warning MSB3061: Unable to delete file "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release\proxydriver.dll". The process cannot access the file 'C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release\proxydriver.dll' because it is being used by another process. {log="C:\WINCE800\build.log(40865)"}
  C:\WINCE800\public\common\oak\misc\buildrel.proj(501,5): error : Error cleaning up flat release directory "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release".  Unable to delete the following file(s) "C:\WINCE800\OSDesigns\OSDesign9\OSDeisgn9\RelDir\VAR_SOM_AM33_ARMV7_Release\proxydriver.dll".  Please make sure there are no other processes using these file(s) and try again. {log="C:\WINCE800\build.log(40870)"}
BLDDEMO: ERROR: Error(s) in buildrel phase. {log="C:\WINCE800\build.log(40877)"}

 

Solution:

You have the Release directory open in a command prompt or File Explorer.  Close them.