Where do you put the command? You have to put the
ip default-gateway xxxxx in the global configuration mode not in the Vlan interface.
This is manual IP assign guide.
This E-Book is Catalyst 3560 Switch Software Configuration Guide from cisco.
May be you have enabled ip routing if so disable ip routing (no ip routing) and use the command ip default-gateway xxxxxxx .
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Or, if you need IP routing enabled, just add a default route to your router.