I added a temporary reference to Microsoft ActiveX Data Objects latest version I see in the list. This has brought a newer version of Interop.ADODB.dll in the obj directory. I was then able to replace that 6.1 version on top of the 6.0 version. Then, I removed the reference to Microsoft ActiveX Data Objects I just added. That warning is now gone.
I need to do the same now for Interop.CDO. However, this one is the same version as the actual one I have.