I was having same problem.
Running kodi 15.2 on Android. Stalker client nfps 0.8.4. It would say channels not loaded but sometimes they were there but with no guide. This was my own fix.
Disabled live tv. Cleared cache. Went into the guide and cleared database. Came out of the settings and cleared main cache and purged packets. Logged into my iptv66 account and changed my MAC again. There was an option to reset iptv so I did that. Changed my MAC again for good measure, only one digit. Went back into kodi. Changed my MAC in stalker client nfps so it matched my one linked to my donation. Changed the timeout to 120. Then enabled. Went back into live tv then enabled again. It worked for me first time. About an hour later I got the error message again so I went back into live tv, cleared cache and tv guide database and all is good again.
I think as they change and upgrade their servers you might get a bit of hit and miss but the above worked for me after several hours of messing around. Hope this helps