Cannot connect to SXT with MAC - Timeout

Hi
I have a network which is built using Mikrotik devices, from RB750 to NetMetal. There are some SXT links connecting some segments of this network. All of these work fine, except two SXTs which are linked and working fine as bridge (Installed by someone else). They have no IPs (0.0.0.0) and there is only one way to connect to them - MAC. But when I try to do this, I get timeouts. I have tested this from two different stations (Windows 7 64 and 2008 R2 64) with firewall and antivirus turned off. I can’t even MAC telnet to these boxes from other Mikrotiks on the same LAN segment (says “Disconnected” after providing username and password), but can MAC ping both.
Any ideas how to fix this?