disable maximum password length on Windows Server

Im not sure about disabling it, It not sure if you want to degrade security on the server.

Start a command prompt as administrator in windows

Run the following command:

net user MyUser MyPasswordIsReallyLongIs36Characlong /ADD /Y

For a domain user:

net user MyUser MyPasswordIsReallyLongIs36Characlong /ADD /DOMAIN /Y 

Should fix the problem.

Run rsop.msc on the machine that is giving you the issues. Then look under:

Computer Conf > Windows Settings > Security Settings > Account Pol > Password Pol

Under there, it will show you Source GPO that is setting the restriction. Then you can open Group Policy management and find the policy needed.