From Nikon:
Changes from Firmware Version 13.001 to 13.002
- Fixed an issue that in extremely rare circumstances would result in the SB-500 not functioning when used with the following cameras that support the Nikon Creative Lighting System:
- The D5, D4, D4S, Df, D810, D810A, D800, D800E, D750, D700, D610, D600, D500, D300, D300S, D7200, D7100, D7000, D5600, D5500, D5300, D5200, D5100, D5000, D3400, D3300, D3200, D3100, D3000, D90, D60, D40, and D40X
- The COOLPIX A, COOLPIX P7800, and COOLPIX P7700
Download: Nikon SB-500 Firmware v.13.002
B&H carries the Nikon SB-500 AF Speedlight.