Expected Behavior

If you choose a different drive to save to, such as a second hard drive or a usb drive, it should save successfully.

Actual Behavior

If you choose anything other than a location on the c:\ drive it will fail to save and throw an error.

Steps to Reproduce

On Windows, connect to a usb thumb drive or external hard drive
Create or open a project
Choose File > Save to your computer
In the file browser that opens up, navigate to the usb drive and try to save it.
Note: an error appears (see screenshot above) that says

Save failed:
D:[file name].sb3
EPERM: operation not permitted, mkdir 'D:'

Operating System and Browser

Windows 10. Can not reproduce on Mac.