David,
Thanks for the answers. More results of HP 40G DAC cable are as follows. A Switch and N Switch are made by other vendors. It looks like DAC cable has more compatibility issue than Fiber transceiver.
1. N Switch to A Switch => Connection
2. 5900 to N Switch => No connection
3. 5900 to IXIA => No connection
4. 5900 to Spirent => No connection
5. 5900 to IXIA => Connection with HP SR4 transceiver
Jeff