The remote computer refused the network connection. (code: 1225)

Thank you
UrBackup running on Windows server 2019. I have changed UrBackup service to run as user with access to shares as noted. So far everything is working as expected. However using the GUI at UrBackupsvr:55414, and trying to mount a backup, I get this …

Mounting image failed. Please see server log file for details.
Error creating ImDisk device. The remote computer refused the network connection. (code: 1225)

What credentials is it using during the mount and where can I change them?

Thank you