Time Machine Error 45

What is Error 45 and how do I fix it? Time Machie Backups are on an external HD, network connected drive (Ethernet). Time Macine has always worked for me but there have been occasional hiccups with accessing the disk. I can usually fix this easily by opening the backup folder in a Finder window, then Time Machine “sees” it and gets to work.

Today, that didn’t work and the message said “Error 45” and nothing else, except the network address of the backup file and "could not be accessed". (Note: the failure flag just appeared again as I write this - same message.)

Thank You, GCF

MacOS Catalina, V. 10.15.3

Model Name: Mac mini

Model Identifier: Macmini7,1

Processor Name: Dual-Core Intel Core i5

Processor Speed: 2.6 GHz

Number of Processors: 1

Total Number of Cores: 2

L2 Cache (per Core): 256 KB

L3 Cache: 3 MB

Hyper-Threading Technology: Enabled

Memory: 16 GB

Boot ROM Version: 246.0.0.0.0

SMC Version (system): 2.24f32