We have a custom object in Salesforce called Account Campaign Member. I associates the companies relevant to the campaign (there is a lookup field called Account which connects Account Campaign Member with Accounts). We would like to be able to have the report which will show us all contacts which sit under the Account associated to the Campaign by Account Campaign Member object.
However, I can't build such report type. Could anyone help me with this please?
On
It sounds to me like you need two different things here: first, you need to make a new report type (Accounts with and without Account Campaign Member, or something of the like).
Then, you need to create a joined report, joining your new report type to the existing Accounts with Contacts report type. Filter to display what you want to display, and you should be good to go.
On your custom object description page, please make sure that "Allow Reports" is checked so that the Salesforce Report Writer has availability to your custom objects. If your relationships are set-up properly, you should have access to them from within a report created with your custom object.