Can't open SD file from task in FreeRTOS

Other Hardware Storage
1

The statement

File f = SD.open(filename, O_CREAT|O_WRONLY|O_TRUNC);

opens a file when I do it from setup before I engage the FreeRTOS scheduler, and I can write the file from an rtos task.

However, the same statement returns false when I execute it from within an rtos task, indicating that it created no file.

I'm using an AdaFruit Feather-M0, the FreeRTOS port for SAMD21 architecture from BriscoeTech, Inc., and the

Sparkfun SD driver version 1.2.4.

Any help will be greatly appreciated.

--Mike