I am unable to upload file here on forum.

This is what I have tried. When posting reply to a thread:
-> Advance -> "Attachments" -> Add Files --> Added zip of 9kb having KJB and KTR --> Click Upload Files --> red (!) giving no useful info
Result file is not uploaded.

I am on mac and it is happening with both Firefox and Chrome.

Any ideas what I am doing wrong?

If this is not best place to post this, please let me know where should I post this.