Some ex5 failed to run in latest build 3756

Build 3756 is a "Beta" build. The latest officially released build is 3661.

If you don't want to be a beta tester then don't connect to MetaQutes demo trade servers. Only connect to reputable broker's trading accounts.

I got it, thank you Fernando.

Hi,

   I cant find reputable broker who provide MT5 release version with demo account, could you  recommend one? thanks.

It depends on your country.
For example - if "reputable broker" = broker which is having the license from the government so there are many reputable brokers.

For example - in China.
You can check the reputation of the broker with the government/SAFE (with State Administration of Foreign Exchange in China),
and as I see - there are many brokers (incl well-known Metatrader brokers) are working in China having the permission/license from SAFE,
and many of them are proposing MT5 together with demo accounts.

Same with other countries ...

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Because the recommendation of the brokers is prohibited on the forum.
And you can read this key thread, for example: Broker selection