There are a couple of reasons why this could be the case...
The machine you're using is not compatible with SDXC, or specifically the
exFAT file system which is required by the SDXC standard.
...or you are shooting in a file format that the machine cannot understand.
Most machines should be fine as this was more of an issue back in the early days of SDHC, so the more likely issue will be shooting in raw. The best way to get around it is either to convert raw files manually in-camera (if you only have one or two), or if you want to cover every image then use the
RAW + JPEG option to create a copy of each picture in both formats as you shoot.