[cvsnt] "cvs commit -r " problem

[=?ISO-2022-JP?Q?=1B=24B8t=3F=2E0B=1B=28B=28Hsin-An_Hou=29?=]

Hi all,
   i want to change the revision of some files. i use "cvs commit" command 
to change the revision of file as the following in WinCVS:
cvs commit -r 2.1 test.v
   
   then a text file is poped on the screen, and it shows the information, 

CVS: ----------------------------------------------------------------------
CVS: Enter Log.  Lines beginning with `CVS:' are removed automatically
CVS: 
CVS: Committing in .
CVS: 
CVS: Modified Files:
CVS:  Tag: 2.1
CVS: test.v 
CVS: ----------------------------------------------------------------------

while i close the text window, the gui is suspended until i stop CVS 
manually. after i stop CVS, an error message shows up

error message: 
Log message unchanged or not specified
a)bort, c)ontinue, e)dit, !)reuse this message unchanged for remaining dirs
Action: (continue) cvs [commit aborted]: received interrupt signal

and the revision of file isn't changed. 

How to commit revision correctly?
i use WinCVS 2.0.2.3 (Build 3) & cvsnt 2.0.51.0

thanks in advance 

Best Regards

Amistad Hou