Cannot Verify The Source Of The Update

[Mymymi]

Any help would be appreciated , non-techy here ! I have a redmi note 2 that I got with 66.77.33.00 -adware/bloatware fitted as standard . After much trial and error I eventually managed to get myself to miui 5.9.10 Beta . In 'updates ' , I have miui 6.1.29 weekly 696.35M showing . But when I try to update I receive 'cannot verify source of update ' message.
I've looked around and found different suggestions for the cause of this -conflict between roms and server issues . Could anyone shed any light on this , please - hopefully in words of one syllable ! Rationally , I don't understand why the system is offering something it can't fulfil

 

[Mymymi]

Anybody ?

 

[Mymymi]

Ok , no takers... could I just download this rom , rename it and use recovery -will that work ?

 

[Mymymi]

Give you a quick update -not that anyone seems to care ! ; ) Tried several times to update to 6.1.29 with no success-repeated source verification failure . Tried official global -same story . I read somewhere to delete earlier downloads -so I deleted the Honorbuy 5.9.10 beta , then 'updated ' it again from the pc , hoping it would be like a fresh start . Once that was done i clicked update for 6.1.29 , which must have taken at least 7 hours to download , and that resulted in the same failure message . Was just about to put the phone away when I noticed that the 6.3.31 ota was available -what the heck , clicked on it , downloaded it and it installed !!! For the life of me I can't understand this , but I am so pleased to be back on otas , though I might have wanted to stay on 6.1.29 a bit as it seemed so well received .
One thing though , all I have so far added to the phone are my google contacts which were ported when I set up the account , and the update zips , but I have less than 9 gb memory left -does this sound right ?