[Romeo.Clavet]

I found one solution, I hope it will help you.

In my case it was the solution at the user configuration level on the BB server.

As per HTTP Error 503: Service Unavailable is displayed when attempting to open a web page in BlackBerry Browser:

Environment
* BlackBerry® Enterprise Server software version 4.1
* BlackBerry Device Software 4.0 to 4.2

Problem
When attempting to open a web page in the BlackBerry Browser, the following error message is displayed:

HTTP Error 503: Service Unavailable
The server is currently unable to handle your request due to a temporary overloading or maintenance of the server. Please try loading a different page. Contact your service provider if this problem persists.


Cause
There are multiple causes for this error.

Summary of Causes
1. The BlackBerry Mobile Data System (BlackBerry MDS) is not enabled for the BlackBerry Enterprise Server and the BlackBerry device user account.
2. The web site that the BlackBerry device user is attempting to access is not available. For example, the proxy server is not configured to allow access to that web site.



Resolution
Complete the appropriate resolution for your cause.

Cause 1
The BlackBerry Mobile Data System (BlackBerry MDS) is not enabled for the BlackBerry Enterprise Server and the BlackBerry device user account.

Resolution
Enable the BlackBerry MDS Connection Service for the BlackBerry Enterprise Server by completing the following steps:
1. Click the Server Configuration tab.
2. Expand Service Control & Customization.
3. Click BlackBerry MDS Connection Service.

Enable the BlackBerry Mobile Data System for the BlackBerry device user account by complete the following steps:
1. Click the User Configuration tab.
2. Select the BlackBerry device user account.
3. Expand Service Access and clickEnable Connection and Collaboration Services.

Cause 2
The web site that the BlackBerry device user is attempting to access is not available. For example, the proxy server is not configured to allow access to that web site.

Resolution
On the Proxy tab of the Mobile Data Service Properties window, set a Proxy Mapping exception. For instructions, see the BlackBerry Enterprise Server 4.1 System Administration Guide.