[CCLOUD.COM] Internal server error:500

Why is it that with every 200 files uploaded through the WEB interface, 2 files (1 percent) are always “rejected” to be uploaded due to an “Internal server error:500” message?

Really, EVERY 200 files there are always 2 random files not uploaded.
I have already uploaded 4 groups of 200 files each, and with each group uploaded, I always get 2 files with upload error.