You can normally use whatever RCP username you wish, with the exception of Windows platforms... in that case, the SYSTEM user is used by the RCP daemon on Windows by default. The key is that the user 'allowed' by the rcp host daemon, is the same as the user trying to execute the rcp operation. If your CW server is a Windows machine, I would suggest setting the Catalyst machine to use SYSTEM as the rcp user.
Here is a link to setting the rcp username on a CatOS product (I chose the 6500, version 6.1 as an example):
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sft_6_1/cmd_ref/setsn_su.htm#1083147
Cheers,
Curtis