Dick Lipton has a blog post that motivated this question. He recalled the Stark-Heegner

Theorem: There are only a finite number of imaginary quadratic fields that have unique factorization. They are $\sqrt{d}$ for $d \in \{ -1,-2,-3,-7,-11,-19,-43,-67,-163 \}$.

From Wikipedia (link in the theorem statement above):

It was essentially proven by Kurt Heegner in 1952, but Heegner's proof had some minor gaps and the theorem was not accepted until Harold Stark gave a complete proof in 1967, which Stark showed was actually equivalent to Heegner's. Heegner "died before anyone really understood what he had done".

I am also reminded of Grassmann's inability to get his work recognized.

What are some other examples of important correct work being rejected by the community?

NB. There was a complementary question here before.