Windows Server: file system limitation

We are developing an app for tablet which uploads and saves photos taken by the user. The problem we are suddenly meeting is that photos are not saved anymore in our directory in our Windows server 2008 r2 standard, but they remain in TEMP directory: we get this error:

0x80070299 File system limitation. Not possible to save file in directory.

but the disk is very very little defragmented (8%); we have also run chkdsk but no error is shown. Our hard disk is NTFS. Do you know how we can discover the problem? Moreover in that directory it seems to be possible to create files, but not to copy them in it.