Looks like you changed or deleted the log file without adjusting the entry in the cleanup dialogue.
My copy of Trados 6.5 has recently started to throw up an error message when I try to clean up a document, number 50104 and it says that the file cammot be found or the name has been changed, even tho I had the file open just seconds ago.
I have reinstalled it but that made no difference. I looked on trados support for anything about this error and there was nothing.
If you enter the error number in the Trados Knowledge Base, you will find KB Article 686, which explains the error and the remedies.
Note that you could have also found a related topic by using the ProZ.com forum search for "error 50104".
The last job I did I had to clean it manually - deleting the source text line by line!
Not necessary either - there's a macro for that. Search the forum for "Tw4WinClean.Main".