I have been struggling with this same issue for several weeks using Project Pro 2010 and have finally found a solution. I’m sorry to resurface such an old topic, but I’ve been unsuccessful trying to find an answer on Google.
To create dependencies (links) across different projects, Microsoft says you have to open both projects and write the predecessor’s <Project Name><Task #> in the ID column of the Predecessors tab of the Task Information window you wish to link. Actually, what you have to do is to write this same string (<Project Name><Task #>) on the Predecessors Column just there on the Tasks Pane. Don’t double click the Task Row or else you’ll be taken to the Task Information window. You don’t want to go there. Just write it there on the Tasks Pane. If you have other predecessors, just add the string the same way you add predecessors, that is putting a coma between tasks.
For example, in my Project1, if I want to put as predecessors tasks #22 and #33 of the same Project1 and a task #44 from Project2, I’ll just write:
In the PREDECESSORS COLUMN OF THE TASKS PANE. NOT THE PREDECESSORS TAB OF THE TASK INFORMATION WINDOW. Sorry to use all caps, but this seems to be a bug in Project Pro 2010.
The string varies if you are using an Enterprise Project Management solution (EPM) such as Project Server. If a project is stored locally or on Project Server, the string to use is this:
Project stored locally on the PC: <Project Name><Task #> (example: Project1/1)
Project stored on Project Server: <><Project Name><Task #> (example: <>Project1/1)
This is just another reason why MS Project is such a not user-friendly piece of software. Why make things easy and intuitive when you can make them difficult and hard to understand? I once had the need to delete a calendar of a Project file. I had to Google that. That’s not user friendly at all.
I hope that users facing this issue find their way to this solution. Google has no other answers regarding this issue.