I run Sygic, and for the most part, am very happy with it.
But it suddenly stopped working one day, and instead presented a screen with the message "SD card access denied" and an OK button.
In case it helps anyone else, here is how I fixed it.
First, Sygic is on /mnt/sd/mmcblk0p11
I tried remounting that rw:
mount -o rw, remount -t vfat /dev/block/vold/259:3 /mnt/sd/mmcblk0p11
Starting Sygic, same problem.
Looking at dmesg, I see "error fat_free_clusters deleting FAT entry beyond EOF"
Ahh, a file system error. Let's fix it.
It found an error and asked me to fix it. To which I reply "y".
Now Sygic works again!
To perform the above, I was root in a terminal window, sitting in my car, using the onscreen keyboard.