INVITE, 401, INVITE and 491 :s

HI everyone,

I’m testing an Asterisk server with SIPp.
When I send an INVITE request to the Asterisk, it answers me with a 401 answer.
Then, I resent the INVITE request with the credentials to be authenticated.

However, even if I’m authenticated (no 401 answer), I received a 491 Pending Request.

I know that according to the RFC, it sends this message cause it received a previous INVITE message within the same dialog but it’s because it asks me credentials that I need to resend an INVITE.

How can I resolve this issue?
Best regards,