There, when I use git to push my code to gitlab, it actually succeeds and I can see my renewed code from gitlab web interface.
However it keeps returning an error message: "No supported authentication methods availabe(server sent:publickey, keyboard-interactive)". I don't understand this.
I have another project hosted by gitlab also. I don't have any problem on pushing code from this project. I wonder what could happen to the first project.
Please clarify me from this mess.
Regards, Alex
You are seeming to use a git URL for pushing/pulling.
In order to get this working you need to load your PuTTY key into the PuTTY agent (pageant; TortoiseGit usually does this automnatically if you have configured a PuTTY key for a remote).
Another way is to configure a PuTTY session (or modify the default session), cf. https://tortoisegit.org/docs/tortoisegit/tgit-ssh-faq.html#tgit-ssh-faq-defaultkey and https://tortoisegit.org/docs/tortoisegit/tgit-ssh-howto.html.
A third way could be to switch to a https URL for remote operations.