R2 Beta Configuration - Business Rules Engine - Service Account Er

Hi,

I am trying to install R2 Beta. I have 2 machines (A and B). My database 
server for all BTS databases is B and BTS server is A. The server B has
SQL 
Server 2005 (with SP2). I successfully installed BTS R2 Beta on A. During
BTS 
custom configuration on A (with B as database server), I am trying to 
configure BizTalk Rules Engine. I checked "Enable Business Rules Engine on

this computer" and filled window service user account information. The 
account is valid (and I used it for other services within BTS
configuration) 
but I get following message:


Specified argument was out of the range of valid values.
Parameter name: ****t (System)

I am clueless as to what this error message means. Any help is
appreciated.

Thanks.