I am on my second SPA400 in as many weeks. I thought the first one had a problem because after doing some configuration it would start re-booting itself on approximately 10 ~ 15 second intervals. I suppose I don't know for sure that they were re-boots, but the SPA400 would lose it's connectivity for a bit, then it would come back for a bit, then lose it for a bit, etc. This was verified by running constant pings to the SPA400.
With both SPA's, they seemed to work fine out of the box with the exception of multiple out-bound calls not working (later fixed by altering the ground-loop start setting). However, following the instructions I upgraded the firmware to 22.214.171.124 and that's when the problems started.
This is apparently random as you may configure any number of things on the SPA400 before the re-boot cycle starts. It doesn't seem to matter what you configure, either. Sometimes you configure option X and it works fine, then later you configure the same option and the cycle starts.
Once it starts, the only way I have found to fix it is to catch it while it is up and do a factory reset on the device (you must work quickly because you only have a few seconds). Then you begin the process all over again.
I also upgraded to the beta firmware of 126.96.36.199, but this didn't fix the problem.
Again, this behavior has been consistent on both SPA400's. At this point I am reluctant to make any configuration changes for fear of it starting to re-boot itself over and over again, but my configuration is less than optimal (default passwords, DHCP, etc.).
If someone could help, I'd really appreciate it.