I recently struggled with an App-v problem (4.6) which kind of difficult to find out. When making an package and customizing it with more icons (such as MS Excel, MS Word or MS Outlook for example) and saving the package will result in an error:
Encountered a sharing violation while while accessing Q:\applicationname\VFS\CSIDL_LOCAL_APPDATA\Microsoft\Windows\Explorer\thumbcache_idx.db.
You can (re)package this over- and over but it won’t help. The only solution for this is by opening the Task Manager and close down explorer.exe from the processes. Then you’ll need an elavated cmd.exe and go to C:\Users\Username\AppData\LOCAL\Microsoft\Windows\Explorer. Here you will need to delete the file thumbcache_idx.db.