1. A data processing apparatus for executing, in response to a processing execution instruction transmitted from an information terminal to the data processing apparatus via a network, processing in accordance with the processing execution instruction, the data processing apparatus comprising: a monitoring unit configured to monitor and determine a storage of the processing execution instruction transmitted from the information terminal to the data processing apparatus via a network; a first determining unit configured to determine a protocol used in transmission of the processing execution instruction; a second determining unit configured to determine whether an error caused during execution of the processing is regarding a file-sharing function or a processing managing function; a converting unit configured to convert error information into the error information such that the error information is compliant with a general-purpose protocol for utilizing the file-sharing function and indicates that the storage of the processing execution instruction is not successful even if the storage of the processing execution instruction is successful, when the first determining unit determines the protocol is the general-purpose protocol for utilizing the file-sharing function and the second determining unit determines the error is regarding the processing managing function; and a transmitting unit configured to transmit the error information converted by the converting unit to the information terminal that has transmitted the processing execution instruction using the protocol used in transmission of the processing execution instruction.