Unable to save to sd card

[pash02]

Hi every so often i get the message " Unable to save file to sd card so default storage has been changed.
This is when i take photos yet my sd card has 5gb spare and my music plays ok.
The phone is a 5 month old S7 on android7.
Why is this happening?
The sd card is about 4 years old and used to be in my S5 mini.

thanks

[BandOfBrothers]

As a process of elimination can you insert your Sd Card in another phone to see if it works Ok. 

And perhaps if possible try another Sd Card in your phone.