When trying write the contents of a file created during the build to disk, emake was unable to open the file identified by the path in the message. The system error message provides additional detail about the specific cause of the failure. Note that this message specifically indicates an error encountered when opening the temporary file created to store the file contents in emake’s temporary directory, not the final location of the output file in your build tree.
Because the error involves an external system in this case (the filesystem on the emake host), the list of possible causes for this error is virtually limitless: a corrupted filesystem; hardware failure; insufficient permissions; and so on. Refer to the specific OS error message to determine the cause of the failure.