Unable to Copy Backup Files to a Share

Hi experts,
This is really a Windows Server issue. I'm trying to manually copy a backup file form one server to another. Manually un tat I'm copying via Windows Explorer by drag/drop.

On Server A, I mapped a drive to Server B. I'm in the Local Admin group on both servers.

When I try to drag the file to Server B, I get
"File Access Denied. You'll need to provide administrator permissions to copy this file.' I click OK and it then presents "Location is not available"

(It's worth noting that for files I create, say a Text file into the same folder, I CAN copy that file to Server B. It's only the .bak and .trn files I can't copy - these were created by the Agent backup job.)

This is a new issue, I was able to copy backup files to Server B a few weeks ago.
Does anyone have any ideas? Thanks

for testing, try renaming the back up file. what happens?

No change. Same error.

So maybe that file is locked by the backup process