This issue is often, but not always, related to saving to the SD card. There are a couple solutions you can try:
We'd first suggest that you do a reboot of your device (hold down the power button, press the "Power Off" button that appears on screen, then hold the power button down again to start your device), and then once the device OS has started up, try to save the game again. In most cases this should resolve the issue.
If rebooting the device doesn't solve the problem, you may need to try reinstalling the game (and possibly rebooting again afterwards).
When installing, we highly recommend you do so to internal storage instead of an SD card, as certain devices may have compatibility issues with saving The Bard's Tale to SD.