Problem attaching files to nodes with Services
try adding more data to the attached file (it might be that fid and filename is not enough I can't find the example I used a long time ago, which had a similar problem):


alt (might be required in general or only if marked as required in bundle)
title (might be required in general or only if marked as required in bundle)
uid
filemime
uri
status = 1
display = 1


Some references I could find quickly:


https://stackoverflow.com/questions/5129559/attaching-image-files-to-nodes-programmatically-in-drupal-7
this answer: https://stackoverflow.com/a/19930610/1158887
https://drupal.stackexchange.com/questions/120078/is-it-safe-to-reuse-the-fid-file-id