I had the same problem. It was complicated by the fact that I have two instances of SSRS running on my system one is 2005 the other 2008, and I thought I knew the 2008 instance's name. I had accidently typed the service account name when I actually needed to type in the Virtual Directory. I resolved this by finding the exact name I needed. I started Reporting Service Configuration Manager, conected to my instance, clicked on the "Web Service URL" to find the correct name. In my case, I needed to replace http://computername/Reportserver$MSSQL10/ with http://computername/Reportserver\_MSSQL10/. This now allows me to deploy (without prompts).
-Will
