Every time you choose to View Output in Notepad the Product Mash hangs and has to restarted.
The reason why the Product Mash appears to hang is that it is waiting for you to close notepad. This is done for the following reasons:
1 So that when the file is being viewed it can't be re-mashed. For some feed viewing programs (e.g. Excel) this locks the file and a feed creation error is shown.
2 If you are creating more than 1 feed at at a time (e.g. 10 feeds) you are not shown 10 files all at the same time.
Once you are happy with the feed output you would normally not view the output. You would click Mash now followed by Upload Feed or you would automatically Mash and Upload your feeds (see Automating the creation and uploading of feeds for more details)