Hello redxdev,
I was just able to add a 4.10 Preview 3 project to a Perforce workspace and then connect to Perforce through UE4 without an issue. Is the project that you’re trying to connect to Perforce with already checked into Perforce or is it not added yet? Can you let me know how your file structure is set up?
Also, what OS are you using? It could be a factor.