Linksys PAP2 in freeswitch -- 2

Hi, we have a new freeswitch server that is working fine with some SIP clients and one trunk working succesfully. We can register an android phone and softphones, but for any reason, we can't register none of the both Linksys PAP2 devices that we have. This is not the famous G729 issue, also tested using just PCMU and PCMA (ulaw /alaw codecs) but nothing. Also, those PAP2 devices work fine with other external SIP accounts of other providers. The log in freeswitch say this: 2015-03-23 18:28:03.842108 [WARNING] sofia_reg.c:1742 SIP auth challenge (REGISTER) on sofia profile 'default' for [1000@[login to view URL]] from ip [login to view URL] And nothing else, the PAP2 show this in the main info page: "Can't connect to login server" Also, this PAP2 device can connect to other SIP accounts in other providers with asterisk or freeswitch. I guess the problem must be in any of the settings of the SIP proviles Any idea about what to do ? Is this any variable that can be adjusted in SIP profiles ? We want to know what's wrong and how to fix in case of future similar problems. Thanks