things to try....
-change server URL Portal (do this at server website)
-use the complete Portal URL
-remove credentials from the server setup menu
-reset iptv at website
http://iptvtalk.net/showthread.php?37227-Server-Setups-with-or-without-Credentials
I strongly suspect that these issues are arising due to something with your ISP or some where along them lines.
The server is not blocking any IPs or any server codes or MACs (unless that MAC is already in use).
Changing the Portal usually works to fix it, but then there are reports that after a time the new portal is blocked as well and another portal change needs to be done.
This sounds an awful lot like something is affecting the connection at the ISP end of things.
Concerning the MAC, you do not have to let the website generate you a MAC.. You can use other means, as shown in the linked thread below
http://iptvtalk.net/showthread.php?15280-MAC-generater
Or you can simply create one yourself, as long it has the correct 6 digit prefix and all 12 digits must be from A to F and or from 0 to 9
And has correct format...
-correct-
00:1a:78:1f:2f:3f
-incorrect-
00-1a-78-1f-2f-3f
00,1a,78,1f,2f,3f
00 1a 78 1f 2f 3f
If you are using a Dreamlink or a Buzz or a Global or an Avov receiver then the MAC is the receiver's iptv application's MAC
That MAC is the one needed and is shown on the underside of the receiver on a sticker or in the iptv application's menus or possibly in other menus as well.