If one version of Underfoot, as an example, gets disconnected and another doesn't then you should look for the differences between them.
If one of you generates a sfv file using something like
http://rapidcrc.sourceforge.net/index.html the other one can use that to compare which files don't match it. Things like the spell file, maybe some UI files, zone files, etc. If it is only a client issue then something that's different between the two should be the problem.