Opening workspace created by someone else

I am new to soapUI (recently purchased Pro). If I create a workspace and save it a network drive I can open the workspace and all the projects are available.  When my co-worker save a workspace to the same location, the projects are not available when I open the workspace.  They all appear with red x's in front of them.  Reloading the projects does not work.  I have to actually reimport the project to have access to it.  Can some one explain to me why this is.  I am also interested in any pointers you have for sharing workspaces and projects among multiple users.

Thanks,
JimJ