SAP has, for a while, provided a new way of installing add-ons via SLD or the Cloud Control Center.
This new package is named Lightweight (LW) and in essence, it is a zip file that contains all the necessary files for your add-on.
The installation process is simple and requires only a few clicks, but there is one caveat, often overlooked.
The installation itself (the unpacking of the zip file) is performed by “the system”. And to do this the system requires the SAP Business One Client Agent service to be running on the machine where we want to install the add-on. It also requires that the windows account the service is running on has the necessary permissions to do its work.
Normally the service is installed to be automatically started and run under the Local System account. This gives the service all it needs to perform the tasks.
If you ever run into the message: “Add-on installation failed” check if the above service is running.
For more information also have a look at the documentation (may require S-User).