Network accounts are unavailable Error

Hi,
I have recently installed 10.7 and tried both upgrade install mode and fresh install mode, but now I’m unable to get connected to my domain. The error message that I’m getting is “Network accounts are unavailable”.
I have found that the domain controller was able to be pinged blindly. The machine was recognized by the computer account corresponding to Active Directory.
The computer gives me a message asking if I wanted to join the existing account.
Can somebody help me with this please?
