How about the available capacity of the SD card?

Did you try another other SD card?

Firsteval - downgrade firmware to 1.3.4 (1.4 firmware is full of bugs and even the tp-link dont share it now) and reset the camera to default setting (press WPS/Reset button for 15 sec) - instruction how to downgrade firmware you will find on link:

https://forum.tp-link.com/showthread.php?108873-NC450-keeps-going-offline!


After that change the memory card. The SanDisc microSD are very flawed. I have SanDisc microSD in my NC450 and I have this same problem. I was using SanDisc micro SD on my phone too - after half year SD cars just stop worknig.
Now i have a Samsung 32GB MB-MD32DA/EUand on both devices and its working perfectly.

A quick solution to your problem is hard/fully forma the SD card on PC (instruction is for Windows 7):
1. put on sd card to the PC
2. right clic on My PC and pres Manage
3. In Storage press Disc Managment
4. right click on sd card and delete partition
5. create a new one and format it

After that SD card should work for some time