Event Log "Child process has exited with code 1" ???

Why ? Should I worry ? How to fix it ?

Although "Child process has exited with code 1" was marked as an error,
it was immediately followed by :-
"Execution of user command succeeded: V:\B\C\MoveDiff.cmd"
and afterwards the Differential image was successfully created and validated.

I often create backup images, both Full and Differential.
Today is the first time I have seen such an error message.

Today is the first time I stipulated the execution of a command before creating the image.
The command fields were :-
command -------------- V:\B\C\MoveDiff.cmd
Working Directory ------ V:\B\C\
Arguments -------------

MoveDiff.cmd held a single command line (with return but no blank lines) :-
MOVE V:\B\C\??D2.TIB V:\B\C\C_old

Should I have concluded that file with the command "EXIT" ?

I hope that this particular error is totally harmless, but I prefer to live error free so would appreciated advice upon fixing if possible.

Supplementary questions :-
I checked the box so any error with my command would abort image creation.
How does Acronis decide whether it succeeded or otherwise ?
Does it test %ERRORLEVEL% to make this decision ?
My single line MoveDiff.cmd is about to become much more complex,
and the last executed DOS Command may have non-standard exit codes.
Should I terminate my MoveDiff.cmd with an appropriate " standard" value with
"SET ERRORLEVEL=0" or "SET ERRORLEVEL=1" ?

N.B. My intention is to create very many and frequent Differential images, BUT I am concerned that if I create 100 differentials upon a single FULL image, it will be impossible to validate ANY part of the archive if any one of those differentials should be damaged. Therefore before creating any differential image, any existing ?D2.TIB differential will be moved to a child sub-directory C_old, so validation will only process the Full image plus the latest differential image - and this validation will be much faster if it does not mindlessly trundle through 99 older differentials which will probably never be needed anyway.

Below is a relevant extract from the event log, showing the context :-

<event code="11" id="17" level="3" message="Priority changed to High priority" module="100" time="1240733738" />
<event code="1024" id="18" level="4" message="Child process has exited with code 1" module="1" time="1240733739" />
<event code="134" id="19" level="2" message="Execution of user command succeeded: V:\B\C\MoveDiff.cmd" module="100" time="1240733739" />
<event code="503" id="20" level="2" message="Analyzing partition 1-9..." module="1" time="1240733739" />