Deleting file from FTp server

I have been trying to delete a file for some time now in a folder. I'm new to this program and the use of FTP, but I don't understand why this won't work. I'm trying to delete a file that is 487kb and attempting to replace it with a different version that is 540KB, however, I cannot delete the first file. I can delete smaller files with no problem but this file I cannot remove from the FTP folder.

[05:45:52] DELE z_modwarfare.iwd
[05:46:07] An established connection was aborted by the software in your host machine.
[05:46:07] Server closed connection

When I try to delete the file... this is the response I get in the log. I can delete other files in the folder, however, this file I cannot seem to remove. I know this is pretty vague but I'm not sure exactly what I'm talking about so if anyone has any ideas or suggestions... would be great.

Ooer. The Only Way I Know (That Works) Is Highlight The File & Press Delete On Your Keyboard. If That Don't Work Then... Meh.

OR If The Files Are Called The Same, Just Drag The One You Want To The Folder. If Not Name It The Same As The One That Wont Go, & Then Rename It When It's Uploaded.