First of all, thank you a lot for resolving the password issue. Today I encountered a new one once I tried to upload a file using cpanel file manager - the window refreshed, but the "upload status" frame remained unchanged, and the file did not appear on the list. What could be a reason for that?

Sometimes when a user uploads a file, your connection could go down (who knows why) then it can stall the file from being uploaded. Many FTP software programs do this but in the sense if you upload a alot of files at once it will just time out and then freeze up; smartFTP has that little quirk.

So the only solution to that really is to re-upload it again, and to make sure you have nothing else going on that could interfere with the connection.

I have a stable connection. Files can be safely deleted from the server, I tried, but they cannot be uploaded. That's not an issue concerning my computer, or my connection.

Ah, I see... for some reason I don't have any disk space left... I wonder why... Before the crash I had like 15 megs free.

Try checking for a malformed file of large size. Then simply delete it to make the relevant space again.