Error when installing addon: "Uninstaller can't be found"

Hi,

I'm trying to build an installer for a addon (with NSIS).

The Install routines run as i expect but when i try to make the call to EndInstallEx("", true), SAP shows up a message saying "Uninstaller for Add-on can't be found" (german: "Uninstaller für Add-on konnte nicht gefunden werden").

When pressing ok, the installer continues and, when finished, SAP says "Installation failed".

Whatever, when I try to re-run the installation, SAP shows "Installation successfully finished" and the addon works...

The question is: Why does SAP miss the uninstaller when nothing is set in the ard-file and where have i to put the uninstaller?

NSIS creates an uninstaller in the installation directory (addons/namespace/addon-name) but the application also complains when I integrate the previously created uninstaller in the ard-file.

What I'm also wondering about: why does SAP say that the installation failed when i call EndInstallEx("", true)? (return value of EndInstallEx is -2 iirc)

TIA

Chris