helper class is not define properly in config.xml of that modules
put the below code this
<global>
......
<helpers>
<custommodule>
<class>Amit_Custommodule_Helper</class>
</custommodule>
</helpers>
...
</global>
Your code should have
<global>
......
<helpers>
<shoppersettings>
<class>YourModulenamaSpace_Shoppersettings_Helper</class>
</shoppersettings>
</helpers>
...
</global>