Drillthrough Report selection not showing

I am trying to link a drillthrough report but the report that I want to select is not listed in the action drop down. This is due to the reports location which is in a different folder.

Reviewing the following:

https://technet.microsoft.com/en-us/library/dd220423(v=sql.105).aspx

I'm still not understanding what I need to do.

Any assistance would be greatly appreciated.

Thank you.

I think the other report must be present in the same solution to come up in the action drop down

The reports in the dropdown are in the same project. I am trying to link to a report that is in a different project but all are in the same solution. Example:

Project1 / MainReport
Project 2 / DrillthroughReport

Thank you for the assistance!