The error explains what is happening: the user account you are submitting to log into CVS does not have write permissions turned on for the repository folder on the CVS server, or for the file in that repository that was checked out.
Where you have to configure write permissions on depends on what protocol you used to connect to the CVS Server (ie pserver, sspi, etc), and the settings in the config file of the CVSROOT folder in your repository, and the platform version of CVS you are using.
