I guess that the AutoRun entry is started in HKLM\Software\Windows\Currentversion\RUN.
This entry is started by csrss.exe in which SuRun does not set a hook into.
You need to change the AutoRUN entry to
"%WINDIR%\SuRun.exe" "C:\Program Files (x86)\ERUNT\AUTOBACK.EXE" C:\Windows\ERDNT\#Date# /noconfirmdelete /days:14
to make SuRun start the backup.
If you mean "Task Scheduler" with the name "Task manager"... You can set the Task to run with elevated rights, or just prepend %windir%\surun.exe as in the example above.