I have experienced this myself. I have found that if the file is quite large, and bigger than the sending limit, it will not be sent.
in the chest, right click the file and click properties, it will give you a value for size, in bytes...
what you then have to do is:
right click avast! tray icon --> program settings --> chest
change the 'maximum size of file to be sent' to fit the file. (it is in kilobytes, so you will need to convert it to kilobytes - divide by a thousand)
round the size up a bit, to give you some leeway...
As for the zipped file, it is most probably because it is not password protected, so avast! scans it and blocks it...
For password protected archives, I use 7zip
www.7zip.comExcept that I use the portable version. This means that it is not installed normally and is contained in a single folder of your choosing, so that if/when you want to get rid of it, you can just delete the folder. I find this much easier than installing the program normally
It can be found here (if you are interested):
http://portableapps.com/apps/utilities/7-zip_portable-Scott-