Error message "Operation not permitted" when trying to do a batch render

[beatrixwillius]

Have the flame path point to the new Dropbox folder.

Click on Batch render for a random flame.

Click on the A button to save all flames. Select the Dropbox folder.

Click on Batch render for a random flame again. JWildfire now wants me to select the Dropbox folder again:

However, after selecting the folder... the dialog to select a folder is shown again. I can only do a cancel and then I get the error message:

If I save the flames to the desktop then I don't get the problem. I've also tried to add a batch render after getting the error and then it worked again. But with the Dropbox folder I can reproduce the problem.