Cannot create a datasource items

I'm trying to use WSS3 & RS 2005 as Integration Mode.
But i cannot create a data source item on sharepoint site library.

If i go to Central Administration > Configure Reporting Services Integration,

I can see the settings, thats mean that the Report Server is available ( i think so )
And also i can create dataources on Central Administration Web site (//servername:12500)

But from my production server web site ( //servername/ ), i cannot create those items.

I received the message

An unexpected error occurred while connecting to the report server. Verify that the report server is available and configured for SharePoint integrated mode.

Can somebody help me to fix that strange behavior.

Thanks.I check the security on the at the below level :

- IIS Site and Application Pool (For Sharepoint:80 and Sharepoint Admin Console:12500)
- Permissions on the folder (Is the same).
- The site Owner is the same on both

The communication from the Sharepoint Admin Console allow any access to RS2005.
For some reason that site have permission to see Reporting Services.

But from Sharepoint Services Portal i can not.

Thanks again.