Return etc. not to be invalid on certain grounds

No, return, statement, assessment, notice summons or other proceedings furnished or made or issued or taken or purported to have been furnished or made or issued or taken in pursuance of any other provision of this Act, shall he invalid or shall he deemed to invalid merely by reason of any mistake defect or commission in such returns, assessment, notice summons or other proceeding is substance and effect in conformity with or according to the intent and purpose of this Act.