Your best bet is probably to follow the instructions here:

http://www.nessoft.com/kb/22

Usually, problems like this are related to bugs in the router's ability to handle multiple outstanding requests.

Another possiblility is to move to an older bios version. I've not yet had a chance to google / google groups on the BEFSX41 to see if others have had problems, but you might do that to see what bios version first introduced this problem (if it was introduced in a bios release), and what version to run for a fix. Changing the settings in the kb above will probably make things work, though.