For each in mapper causing translation issues

In the FTP process in the mapper if we put a for-each loop to append multiple lines to the csv file it errors out with the error:-

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Fault:<soap-env:Fault xmlns:soap-env="http://schemas.xmlsoap.org/soap/envelope/">

<faultcode xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">soap:Server</faultcode>

<faultstring>ICS runtime execution error</faultstring>

<detail>

<ICSfaultVar />

<reason>Translation Error. Translation Error. Error while translating message to native format. Please make sure that the payload for the outbound interaction conforms to the schema and payload size does not exceed threshold. Error occured as {1} :Application Error</reason>

<operation>WriteFile</operation>