SSH connection problem

Hi all! I've a server with six ethernet devices of the same brand. They manage six different networks. I've, also, a SuSeFirewall2 with ssh service open from the internal networks. Everything works well, but sometime I'm not able to connect to the ssh service on the server, even if it forwards the packets (http, ftp...) nicely!!!! All stranges, I noticed, were collisions on two network devices maded, probably, from a damaged switch or samething like! Who know the cause? Anyone may help me?