List of proofs of non-trivial theorems which were unnoticed to be wrong for at least a few years For example, the Weber's proof of Kronecker–Weber theorem.
I would like to know such proofs.
It seems to be important for me to remember that a widely accepted proof might be wrong.
 A: There are many variations on this theme in MathOverflow.  
Widely accepted mathematical results that were later shown wrong
Failures that lead eventually to new mathematics
Most interesting mathematics mistake
How to refer to a theorem that you have shown to be wrong
What are some correct results discovered with incorrect or no proofs
Examples where physical heuristics led to incorrect answers
Oldest bug in computer algebra
Retracted mathematics papers
What mistakes did the italian algebraic geometers actually make 
Italian school of algebraic geometry and rigorous proofs
Can a mathematical definition be wrong
Mathematicians whose works were criticized by contemporaries but became widely accepted later
What are examples of theorem which were once valid then became invalid as standard definitions shifted
Have we ever lost any mathematics
Examples of conjectures that were widely believed to be true but later proved false
Statements which were given as axioms which later turned out to be false
and for good measure 
Smith-Minkowski-Siegel mass formula
Grunwald-Wang theorem
Polygons Flip Finitely: Flaws and a Fix
