When I try to FTP to my website I get a "No space left on device" message. I am well within the space allowed by my ISP. Every other website provided by the ISP has exactly the same problem. Nobody can upload to their website. The ISP's customer support people are renowned for being obtusely unhelpful and so far they are behaving true to form. So I am trying to understand what the problem is so that I can, ideally, tell the ISP what the solution is.

Here is the raw FTP data:

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Users\admin>FTP uploads.webspace.freeserve.net
Connected to upload.webspace.pol.co.uk.
220-webspacem1.svr.pol.co.uk FTP server
($Id: ftpd,v 1.2 2006/09/14 09:11:05 sim onc Exp $)
220-Local time is now 11:45 and the load is 0.12.
220 You will be thrown out after 900 seconds of inactivity.
User (upload.webspace.pol.co.uk (none)): [mysite]
331 User [mysite] OK. Password required.
230-You are using 6.09MB of space, and you have 8.91MB free.
230 OK
ftp> put
Local file C:\xtest.htm
Remote file xtest.htm
200 Data connection will be to [my ip] port 50920
150-Connected to [my ip] port 50920
150 Opening data connection
450-Error during write to file: No space left on device
450 xtest.htm removed
ftp: 215 bytes sent in 0.20Seconds 1.06Kbytes/sec.

CuteFTP can connect successfully, can delete files from the webspace and can upload files of zero bytes (accessing these pages on the web shows a blank page). But uploading a file of more than 0 bytes fails and this is true for new pages and for replacement pages. If the upload is a replacement of an existing page, the existing page is deleted and accessing it subsequently gives a 404.

It has been suggested the problem could be that the UNIX /tmp file is full. I have no idea if this could be the case. Could it?

The server which holds all of the affected websites is Is there any way that I can examine that server, or run diagnostics against it, that will help identify the problem?

Yes, the ISP should be doing all this but they are, frankly, useless and need to be told the answer before they will do anything.