Hi Dab and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, eject and inspect the memory card again. Verify that the lock tab/switch is not set to the LOCK position. Please click HERE to view.
If still a no-go, then try another SD or SDHC or SDXC memory card.
Should the above on any memory card be not corrective, then it would be an internal hardware issue with the TG-4 particularly on the contact pins of the memory card slot.
If so, a replacement would be to your advantage.