HTTP 403 - Forbidden

we have installed SRM5.0 and logged into SRM EBP screen when we press any node like SHOP, system says

"The termination occurred in system SRM with error code 403 and for the reason Forbidden.

The selected virtual host was 0."

"What can I do?

Please select a valid URL.

If you do not yet have a user ID, contact your system administrator"

ErrorCode:ICF-NF-http-c:000-u:SAPSYS-l:E-i:sap5_SRM_01-v:0-s:403-r:Forbidden ,HTTP 403 - Forbidden"

what must be the reason for this error

Arun