Try checking the following threads.....they both have info on similar problems with remote sites accessing centralised servers.....
thread48-231192
thread48-248388
Hope these give you some pointers, it's quite difficult without knowing the overall set-up....???? The 2Mb/s line should be more than sufficient for handling access to the Citrix Server...??? Is this a new site...??? If not, has there always been connection problems or is it only recently that the problem has started....????