What was the modification you made? If everything was working prior to that, then that could well be the cause. I’ve just tested 5.5 with WP 4.1 locally and everything seems to be working fine. What version of PHP are you using?
You can use the ‘set as private reply’ option below to post your login details, that way only I’ll be able to see them. In the meantime I’ll email our developer team to see what they think could be happening.