Hi, Jeffrey. I'll be happy to assist you today.
Sorry to know you're experiencing this backup issue.
Sometimes this issue can be fixed by registering VSS writers again. To perform this procedure, please open CMD as administrator, then paste the following commands:
net stop "Background Intelligent Transfer Service"
net stop "COM+ Event System"
net stop "Microsoft Software Shadow Copy Provider"
net stop "Volume Shadow Copy"
net stop Winmgmt
net stop WSearch
cd /d %windir%\system32\wbem
dir /b *.dll > dlllist.txt
for /f %f in (dlllist.txt) do regsvr32 /s %f
net start "Background Intelligent Transfer Service"
net start "COM+ Event System"
net start "Microsoft Software Shadow Copy Provider"
net start "Volume Shadow Copy"
net start Winmgmt
net start WSearch
del dllist.txt /Q
Finally, try again to backup your computer.
If you need something else, please let me know.