Make sure it's pressed on squarely. Use a crystal press with the right sized dies installed...the bottom one to support the caseback correctly and the top one to bear on the bezel only...not overlap onto the crystal. It's only got to be slightly scue-whiff and it won't turn properly. As mentioned above, lightly lubricate the tension/click spring and gasket with silicone grease before pressing home. It once took me several attempts to replace a Seiko Sea Urchin bezel, but once seated correctly it turned perfectly.