I’ve fixed the issue.

It was a larger Windows problem. Other programs started to fail and I thought the whole PC would need to be reformatted.

However, I did this and everything (including the Ark Client v1.5.1) works great:

-Open a Windows Command Prompt (cmd) with Administrator rights.

-Type: sfc /scannow <enter> Note: This failed when I ran it.

-Type: DISM /Online /Cleanup-Image /RestoreHealth <enter> Note: Keep running this over and over until it says everything is great.

-Type sfc /scannow <enter> Note: Again keep running this over and over until it says everything is great.

-Reboot

Hopefully this works for anyone else with a similar issue. I believe both of these Windows commands work on Windows 8 and up.