Back to My Mac suddenly stopped working

Question

Hello
I have a new iMac and a Macbook about 12 months old, both with Leopard 10.5.3. They are both connected wirelessly via Airport Extreme Base Station acting as a bridge with a 4 port ADSL modem router managing the network.
I have been using Back to My Mac - there was nothing to set up - it all just worked when I enabled it and I was able to access the iMac from the Macbook anywhere in the house and vice versa.
However, I now have the message in the Back to My Mac preference pane that it is not working properly because I need a router with uPnP or NAT-PMP. Nothing has changed, though, on the network. I have looked at the settings in the router and uPnP is enabled, and it was certainly working great before - in fact, I loved it!! It was one of the main reasons I bought the iMac.
I'd appreciate any information. I have a .mac account and everything else seems to be going just fine.
Deborah

Answer 1

Deborah, I just had a similar problem that I managed to figure out with the clues I found on these discussions. My office network had BTMM working fine until we had to replace our DLS modem and then it stopped. The office macs could see and access my remote mac, but I could no longer connect to those office macs.
I recalled reading somewhere, perhaps on a post for an entirely different problem, that both a DLS modem and whatever wireless router you are using can in fact both be trying to distribute IP addresses. I think the problem is called "Double NAT." It doesn't seem to affect the network behavior in any other way (or at least I had not discovered it until my home AP Extreme gave me a warning about the same problem which I fixed a few weeks ago).
When I discovered that the new DLS modem in my office was set to PPPoE instead of Bridge mode, I changed it (my wireless router is set to distribute IP addresses). Still nothing. But then I remembered another post that suggested logging out of my .Mac account, logging back in and turning BTMM off and on. Presto. All is well.