First, How many files do you have and how big are they. This could be because of the size issue and you are running out of ram when its trying to load the data.
Second. Enable the Generate Log option in QVW. Along with the list of fields in the load statement, create one more field like below to identify when the QVW freezes which file is being loaded.
FileName() as LoadingFile
after the freeze, you can kill the process and go check the log which file was being loaded and based that you will be able to understand further as to why this would happen.