I am unable to "Associate Project" to a created Deal. This is the error message I keep being given without any explanation as to what the problem is in terms I actually understand. I have a few that have worked but they seem to have the same settings as the new ones that aren't being allowed so I am unable to find what is wrong with my own eyes. 

The client contact, the deal and project are all listed under the same Account Name and yet, I can't link them anymore. Can someone please tell me what settings I need to be looking at to fix this?