I create 2 projects (P1, P2) and the 2 projects have 2 namespace (N1, N2; N1 belongs to P1, N2 belongs to P2). I could use "using X=N1", but i can not use "using X=N2" at project P1, P1 can not find the namespace N2. I know it can, but if I should change some settings thanks!

BTW, if i put both of the 2 namespace (N1, N2) at P1, then whatever i could use "using X=N1" and "using X=N2".

not really sure I follow *confused* - will re read but perhaps the project you are trying to access from the other project has not been added as a reference in the project, so add a reference to the project/namespace you are trying to access - you should then be able to access it.

example I have 2 projects, 2 namespaces (1 each project), in order for me to access namespace/project "B" from "A", I have to add a reference to project "B" so I can use it/access it.