Cable Forum - Problem uploading other than v small files

I can see this has been discussed before but I have tried most, if not all, of the suggested fixes with no luck. :(

I have been maintaining my web space on ntlworld for 3 or 4 years now, using the FTP "File - Login as ..." facility in both IE6 and IE7, with no problems. The latest fully successful upload was in October and, last week, I tried to do another, but got the failure shown in the attached piccy. Have also tried copying using "My Network Places" - again successful in the past.

It seems to affect all files more than about 300kb and, sometimes, files between 100kb and 300kb. I was able to copy approx 400 small files in one go with no problem at all and am only using about 30Mb of the available 55.

Using WinXP SP2, fully patched from windows update. Plus Comodo firewall, anti-virus and anti-malware

Recent changes are that I have updated the Comodo firewall from v2.4 to v3.0 plus all windows updates. As I can copy small files, I dont think it is the firewall - maybe anyway!

Is this error likely to be meaningful (for once knowing the usual standard of windows messages)? What could cause a file to be locked? I have downloaded Unlocker and this shows the file is not locked!

I have tried it with the firewall, antivirus & anti-malware all closed down. I have downloaded and tried SmartFTP - small files only are OK.

Any help from you gurus out there gratefully received.

Rog