unable to copy files: "not enough space"

Thank you for the information. I had no idea about this!

I enabled http/s for the share in question (and another share, to copy files from). I seem to be missing something. It seems to me I can only copy files across folders within one share. When I try to select a file from share y, copy, then paste it in a folder in share x (through the frontview interface), I get the message "Please select the file(s) first ...".
On the other hand, when I try to copy/paste a file from share x\folder1 to share x\folder2 (something that I am able to achieve through Windows Explorer interface), I get the message "0 files and directories pasted".

Am I doing something wrong?

Edit: I was able to copy/paste a file after creating a new folder: from <share x\folder 1> to <share x\folder new>.
I have realized that while I can edit new folders (copy files to, delete etc.) created using the web interface, I cannot do so, with existing folders. Is there any way to copy files across shares though? How do I test copy a large file (from else where) to share x? I guess I will have to set up a back-up job for that.