what what wrong at animal farm and it is possible to blame anyone?

Technically, everything went exactly as Napoleon planned; he got what he wanted and took control of the farm. If anything might be considered to blame it would have to be the ignorance of the other animals. Countries have been taken over countless times throughout history in just this way. People are promised better than what they have........... but nothing ever get better.

What goes wrong at Animal Farm is the desire for power that Napoleon quickly succumbs to. To blame anyone seems easy enough because Napoleon takes advantage of the fact that he is smarter than most of the other animals and he became interested in his own comfort and success more than the comfort and care of the other animals. Certainly, in an animal fable such as this, the animals have the characteristics of humans and thus give in to the many evils that surround them.

 I believe that it is down to the animals fear of death by the dogs, and their stupidity. If they had the courage or intelegence to stand up to Napoleon who knows what difference it would have made.

At Animal Farm, was what was required was political democracy, improved education and sufficient food for all, not Farmer Jones' Capitalism, or Napoleon's Communist/Fascist dictatorship...

Who is to blame - why it has to be the farm animals who, after being led into a glorious revolution, failed to keep their own leaders in check through their own ignorance and fear of the dogs (the secret police). Despite initially improving the farm animals life-prospects, the animal leadership eventually were able to control everything and the slower, ignorant and less educated animals were left at the bottom with no say, no opportunities for improvement and no share in the farm's prosperity. However at the time they knew no different, they trusted their leaders to do right as they promised but with no safeguards in place, their leaders took advantage and became dictators and were no longer the protectors of the common-good of the farm and its animals welfare. They became the capitalist dictators they originally despised. However by the time the farm animals realised that it was all going wrong, it was too late. They now lacked the courage to challenge and question their leaders and they also lacked the confidence and knowledge to successfully run the farm without them - catch 22.  Human nature at its worst often displays greed and dishonesty, particularly if the humans know that they can 'get away with it' - all too often humanity needs to be kept in order by democratic laws and public accountability.  Otherwise, they tend to succumb to the temptations and excesses that total power can offer - it is often said that 'power corrupts and absolute power corrupts absolutely'...
In the fable, Animal Farm happened and despite being a great idea in principle, in practice it became an out-of-control monster that lost its direction, but that doesn't mean that they shouldn't have attempted the overthrow, after all life under Farmer Jones was just as bad if not worse, just that next time – they need to do a better job!