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But, my database is residing in version 10, not 7. So, I really need to just upgrade the psql.exe to version 10. Actually I don’t know why psql is version 7 and the server for my database is in 10.

Is the 10 you just downloaded the *only* PostgreSQL installation on your system? If you downloaded and installed it from one of the installers provided by partners there should be no version differences (not even with a 7.x, that goes back more than 10 years ago). I'm starting to suspect you have 2 PostgreSQL installations on your system and you're running psql from the wrong \bin folder.

What's the output when you connect via psql?

Cheers

Moreno