Specify the account used to access the existing report server catalog database. This value is required. If you omit this ...

Specify the account used to access the existing report server catalog database. This value is required. If you omit this value, Setup will use the default built-in account for the current operating system (either NetworkService or LocalSystem). If you specify a domain user account, the domain must be under 254 characters and the user name must be under 20 characters. The account name cannot contain the following characters:
" / \ [ ] : ; | = , + * ? < >