What version of RouterOS was on the RB4505? What version of RouterOS is on the RB1100AHx2? Have you exported the configs from both and tried to find what is different between them? You can use terminal to /log print to allow you to copy and paste log entries into your help requests. That will allevi...

Export your PPP, interface L2TP and PPTP configs, and firewall rules. Show us one connection attempt from your logs.

There is probably a rule or interface config setting which should not be set.

There are many possible problems. Too many subscribers for the AP. Other WISP in town changing frequency when they have interference causing this WISP to change frequency causing another WISP to change frequency. If so, they might be able to co-ordinate channels between the WISPs. WISPs tend to use ...

Look at your network interfaces. Did they auto-negotiate the right speed and duplex? Do you have any error counters incrementing on RX or TX?

Can you describe what throughput you get on the x86 vs the 2011?

This thread looks like it has the information you need:

http://forum.mikrotik.com/viewtopic.php?f=13&t=43275

it is on the drawing board. Just do not hold your breath waiting for it, it could take some time.

Having MTR in RouterOS would be wonderful. Thank you for letting us know that MikroTik will work on it.