I would check that HTTP & Verbose HTTP Logging is switched on for your BES, the following instructions may be useful:
To enable HTTP logging for the BlackBerry Mobile Data Service, complete the following steps:
Assuming you are on BlackBerry Enterprise Server v4.1+
1. In BlackBerry Manager, select the <Server Name>_MDS-CS service.
2. On the Connection Service tab, click Edit Properties.
3. On the Logs tab, verify that IPPP logging enabled is set to true, set both the HTTP Logging Enabled and the Verbose HTTP Logging Enabled drop-down lists to True.
4. Click Apply, and then click OK.
You may need to restart MDS_CS service for this to take effect, then test by surfing the internet on a BES connected BlackBerry