sd card for sn9 elite cpap machine

i have a s9 elite cpap machine with sd card i removed the sd card to put in a reader and when i put it back in the cpap it read invalid card and would not show any more sessions my cpap is 1 year old and this is the first time card was removed thanks

Usually, the old "cold start" routine works.
Unplug the power brick from the wall, count to 20, plug back in.
Also, eject the card and then re-insert, making sure it's all the way in.

If you are using a Mac computer small hidden files are placed on the card. As a general practice I always lock the card after removing it from the CPAP machine. Once I am done with the card I unlock it prior to returning it into the CPAP machine. That way the files can not be altered. In both PCs and Macs this practice will prevent a minor error from altering the card.

twostepper,

Another thing to check is whether your computer has somehow gotten infected with a virus. Three years ago when I was using an S9 the computer I had ResScan installed on became infected with some virus or other. The first "symptom" I picked up on was that ResScan would download the data from the card, but when I put the card back into the S9, it would reject it due to some error or other and I would have to erase the card (either on the S9 or on a *different* computer) before the S9 was happy with it.

So if it's been a while since you've run a full virus scan on the computer, that's worth doing too.