On Thu, Feb 6, 2014 at 7:15 AM, Jeff Huettner <jeffhuettner@yahoo.com> wrote:
02/06/14 08:25:55 AM [Insteon::ALDB_PLM] WARN: attempt to add link to PLM that already exists! deviceid=250172, group=11, is_controller=1, subaddress=11

This is a harmless bug, but the outstanding patch will fix it.
02/06/14 08:25:46 AM [Insteon_PLM] WARN: encountered '026225017208297906' from $Niche_lt with command: 29, but expected '026225017205290806'.
02/06/14 08:25:46 AM [Insteon_PLM] WARN: encountered '026225017208297906025025017220f38f202979' from $Niche_lt with command: 29, but expected '026225017205290806'.

This happens, it is a sign of corruption somewhere between MH and the PLM.  We have gone round and round on this mailing list about how this could happen.  One or two errors like this every so often isn't a big deal, MH is robust enough now that it should catch these without issue.  

If you see a lot of this, then you may want to consider taking actions to cut down on potential interference received by the PLM.  This can include, putting a filterlinc on the computer, moving the PLM away from other electronic devices, changing the USB port that you use, or consider getting a new PLM (they can go bad).

Are these most likely due to noisy lines?  I had an all-X10 system working fairly well before I converted over to Insteon starting about 14 months ago, and if anything I'd expect it to be even better now due to removing most of the CFL bulbs in my house.

Both of the errors you have sent are PLM ACK errors.  MH sends a command to the PLM and the PLM responds back with the same command with the byte 06 appended to the end.  Nothing has been put on the power line yet when this occurs.  To me this suggests some noise close to the PLM.  The power supply in my PC was rather noisy, adding a filterlinc to isolate the PC helped a lot.