Density Dependent model

I'm working on density dependent saltwater intrusion model. From previous post I found that needs to choose viscosity incorporated and the extended Boussinesq approximation option for getting salwater wedge.

I have been looking the extended Boussinesq approximation option in the transport setting. I couldn't find the extended Boussinesq approximation word anywhere in the transport setting tool. I choose below options and tried to run the density dependent model. But it shows an error after 30 days run.

I have checked this in other settings tab also. But I couldn't able to find where the specific option setting is located in the FEFLOW problem settings window (see below figure) and how to viscosity incorporated and the extended Boussinesq approximation.

Could you please help to fix this issue.

The settings for the both the Boussinesq approximation as well as for the viscosity looks OK. If you deactivate the checkbox [i]Invoke Boussinesq approximation[/i] you automatically adopt the Extended Boussinesq approximation.

Regarding numerical instabilities I would like to draw your attention to a previous discussion:
http://forum.mikebydhi.com/index.php/topic,2263.msg5242.html#msg5242