A hint when asking questions about script/plugins, supply the source of the script/plugin as otherwise you make us search the internet for random information that might apply.
With that said, the following is based on the assumption that the "CurveBatch" you're talking about is from here: http://gimpfr.org/contrib_photolabo.php#CurveBatch
You need to specify the file extension as JPG not .JPG
With that said, the following is based on the assumption that the "CurveBatch" you're talking about is from here: http://gimpfr.org/contrib_photolabo.php#CurveBatch
You need to specify the file extension as JPG not .JPG