In Virtual DataPort Administration Tool, I have been able to create a base view in Mongodb datasource by the following steps,
1. Created custom data source using Denodo MongoDB Custom Wrapper downloaded from Support Site.
1. Click on “Create base view”.
1. Specify the Host, Port, Database, Collection and Fields and click Ok.
You could refer the section “Creating a Base View” in Denodo MongoDB Custom Wrapper user manual for more details on it.
I would also suggest you to check the log files located in <DENODO_HOME>\logs\vdp\vdp.log and <DENODO_HOME>\logs\vdp-admin\vdp-admin.log for more details on the error.
To be able to download Denodo MongoDB Custom Wrapper from [Support Site](https://support.denodo.com/resources/denodo-connect/list/Denodo%206.0), you would need a valid support user.
Hope this helps.