Issue in accessing two different environments

Hi,

We have UAT and Production CRM deployed using IFD. When I logged into UAT and when I try to access production in parallel it is throwing error below.

"An error has occurred.

Try this action again. If the problem continues, check the Microsoft Dynamics CRM Community for solutions or contact your organization's Microsoft Dynamics CRM Administrator. Finally, you can contact Microsoft Support."

I have to go to Internet Explorer -File - New session and then when I access the production then it redirects to login  page. Why it did not redirect to login initially?

Thanks.