Ax 2012 Clients starts very slowly

Hello.

We are experiencing a problem after we moved our workers to another domain. Thus:

We have AOS installed in a server under the domain a.com. And installed client on a server under domain b.com.

Whenever a client started under the domain b.com, the client opens very slowly, thus, opening client takes 80 seconds or more. But, after the client opened, everything works perfect and no slow mark seen.

We also have a client installed on a server under the domain a.com, and it opens very quickly, connecting the same AOS. On the network, the ping is in good.

Can anyone please give me any idea on resolving this issue?

Thanks in advance.