arabic chracter in display name can't login

[Abuzaid]

after converting the database we discovered that members with arabic characters in their display name cannnot log in ; although

if we create new member with arabic character in his name he can login with no problem

attach screenshot of the conversion:

[opentype]

19 minutes ago, Abuzaid said:

after converting the database

Converted how?

The screenshot doesn’t show much. You would have to inspect the actual user name values in the member table to see potential problems. Whatever you find there would tell what to do next. 
(Having the entries damaged irreversibly is a possibility though.)

[bfarber]

If new user registrations work, but an existing user does not following a "conversion" (or major upgrade like 3.x to 4.x), then it is possible the username characters were corrupted. The only way we'd be able to check is if you submit a ticket with access details.