I have a magento 1.7.x, when i saved only payment section configuration got an error "An error occurred while saving this configuration: Maximum key size must be smaller" on server. while working on local server. Any solutions ?
Which paymetn method are you trying to configure?
Did you installed some payment method (besides the ones that alredy come?)
Can you disable that module and try to save some setting?
I can't answer that without checking the module. Maybe you can ask for support to the module vendor or developer.