Redmine

I use CVS as SCM tool.
When I open the Repository page, following error occurs.

An error occurred when trying to access the repository: No such file or directory - cvs -d :pserver:username:pass@cvshost:c:/user/projectname rlog doc/

I can execute the same command successfully at a command prompt.
Why does this command fail at Redmine?

production.log

Processing RepositoriesController#show (for 192.168.50.22 at 2008-05-21 10:51:18) [GET]
  Session ID: 6cdd0d67daed4bff6e36a7e05d4c0413
  Parameters: {"action"=>"show", "id"=>"myproject", "controller"=>"repositories"}
SCM command failed: cvs -d :pserver:username:pass@cvshost:c:/user/projectname rlog doc/
  with: No such file or directory - cvs -d :pserver:username:pass@cvshost:c:/user/projectname rlog doc/
Rendering template within layouts/base
Completed in 0.64100 (1 reqs/sec) | Rendering: 0.25000 (39%) | DB: 0.00000 (0%) | 500 Internal Server Error [http://localhost/redmine/repositories/show/myproject]