Curious if file permissions are the same as listed in the documentation. Tried upgrading my site and getting a 403 Forbidden error. Seems like there may be a permissions issue, but haven't been able to track anything down so far. Here is what I've done to this point.
I've followed the upgrade documentation located here: http://docs.nopcommerce.com/display/en/Upgrading+nopCommerce
Backed up site files as well as database. Cleaned out the site files, uploaded 4.20 files, copied backup files of wwwroot/Images and App_Data/InstalledPlugins.json and App_Data/dataSettings.json
I've given the correct permissions following the installation guide
For nopCommerce versions 4.00 and above: Some folders were named a differently or missing all together.
\bin\ `Folder didn't exist
\log\ `New folder named 'Logs'
\wwwroot\bin\ `Folder didn't exist
\App_Data\installedPlugins.json (after installation)
\App_Data\dataSettings.json (after installation)