Unable to login to jenkins with valid credentials

[Ghulam Alekuzei]

I'm having trouble in signing in to our Jenkins Server with any valid credentials. First I thought there is some problem with 1 of the credentials, so I turned off the security through config.xml and reset the password through GUI and also proof-checked that passwordhash has changed in config.xml, but still couldn't login through even with the newly changed credentials. How can I fix this problem, it's a security problem if I leave our jenkins server without authentication.