How do I change permissions on my SD Card?

Ensure that the physical lock is open. Some of the SD cards have a physical tang or tab that can be chaned from lock/unlock. Yours may have been inadvertently moved. Can the camera read/write to it?

This worked for me - thanks. had been driving me nuts and I had never noticed the physical "lock" . Thanks

Do you have any other cards, and if so, are they the same?

Drag and drop to trash can. if this doesn't work right click the file to select it and then choose file get info. At the bottom is an option for permissions. click the privilege and make sure it says read & write. If you can't do that, click the little lock on the bottom right, enter your password and try to change your permission to read/write. Once it says read and write, then it should delete.

If the card is not write-locked and is working with other devices, see below.

The card reader is apparently stuck in write-locked mode. I don't generally advise do-it-yourself hardware repair, but one ASC member managed to fix this problem. I haven't tried the fix myself and I can't offer any guidance beyond what's in that discussion. If you cause damage, don't expect your warranty to cover it. I suggest you instead make a "Genius" appointment at an Apple Store.

This advice helped big time. If you do go to "fix this problem" it is going to tell you about a mechanical switch that senses whether or not the SD card is in the lock position. Basically, that switch sometimes gets stuck. Before taking your imac apart, try wiggling the card...I did and after a full afternoon of frustration, voila, my card with "read" and "write".

Hope this helps.