The type or namespace name 'SharePoint' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?) inspite of correct references set.

Are you facing this? and the reference is already referred properly still getting this?

The issue could be .NetFramework version set incorrectly.

Make sure for SP 2013 it is set to 4.5

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If it is not set it to 4.5 and the error should be gone