Connectivity Issues

Ok.. Here is the scenario… I have two remote offices(Location A and Location B) where we use Win Xp Pro through a wired and wireless cable modem connection to get to a third office (location C), which is on DSL using a Linksys router. In location A, I can access location B and location C, through a wireless or wired connection, using FTP or Remote Desktop connection. Now in location B, I can access Location A, again wired and wireless, FTP and Remote Desktop connection, but I can not get to either the FTP or the Remote Desktop Connection from location B to Location C. I have carried the same computer to all three locations, I have changed out routers, nothing…. Has any one ever experienced such nonsense?

Thanks