Could not find schema information for the element 'setting'.

Just come back to my project then suddenly i get 14 messages for no reason

Could not find schema information for the element 'setting'.
Could not find schema information for the attribute 'name'.
Could not find schema information for the attribute 'serializeAs'.
Could not find schema information for the element 'SimpleCoders.My.MySettings'.
Could not find schema information for the element 'userSettings'.
Could not find schema information for the element 'value'.

all from <project>.exe.config

does not seem to be effecting my project but i would like to know why they have suddenly come up and how to resolve it