ERROR the requested URL could not be retrieved

Hello;

I have 2 Blackberry handhelds working on the same BES server.

A 8320 handheld OS 4.5 working properly when i connect a web page via Blackberry Browser but a 9900 handheld OS 7.0 giving the error below. Is there a solution for this error?

The requested URL could not be retrieved

While trying to retrieve the URL: my url

The following error was encountered:

Unable to determine IP address from host name for my url.
The dnsserver returned:

Server Failure: The name server was unable to process this query.
This means that:

The cache was not able to resolve the hostname presented in the URL.
Check if the address is correct.
Your cache administrator is webmaster