Hi SK,
What development tool are you using? CW10.6.4 or IAR or Keil or Other?
Which target are you compiling and downloading?
I'm using Int Flash SramData Debug for the mfs_sdcard_twrk70f120m MQX4.1.1 application.
I write a file....removed SD Card and plugged it back in then typed the file to see it on the terminal successfully.
I then removed and plugged into my Win7 64-bit laptop and could find file, open (NotePad++), see, edit, and save successfully.
I then removed from laptop and plugged into TWR-K70F120M again and could again see file and type file successfully.
You might try cleaning your projects, rebuilding, and re-testing.
Regards,
David