The script file scriptfilename does not exist.
The filename used in the script tag was not found in the asset.
The script tag is used to indicate the name of a script file that will be used with this asset. If that file is not found, this error will be logged. The script file will have an extension '.gs' or '.gse', but the config.txt entry does not require the extension.
If the filename has been misspelled in config.txt then correct the spelling. If the file is located in a different folder in the asset then move the file to the top-folder level. If the file does not exist then the script tag should be removed, along with the class tag and its value if it exists. The functionality provided by the script will not be available.
If this error is reported in conjunction with other errors relating to the script file, then those other errors should be fixed before addressing this error.