Teracopy can't copy/move to or from C:\ to D\

…but does just fine from/to any other drive. I recently put a new win10 install on a new machine. I like to keep my docs separate from the OS, so I divided the SSD into two partitions, C:\ & D:\, then discovered that Teracopy doesn’t want to copy or move files from one to the other, but Windows Explorer will do the deed. With Teracopy, I get either ‘file not found’ or ‘insufficient permissions’ errors.

I have several USB drives plugged in, and moving stuff among them or to/from C:\ or D:\ works as expected. Have tried to set all the permissions I could find on both drives to ‘full control’ but encountered many, many ‘access denied’ messages in the process and no joy. I’m suspecting screwed up permissions but am at a loss as to how to fix that.

In addition, Dropbox and Evernote have difficulty writing to D:\, but other apps do not. If somebody could point me in the right direction, I surely would appreciate it.