Sometimes when uninstalling an application through SCCM, an exit code of 1605 can be returned. This error is returned by the application being uninstalled, rather than SCCM. 1605 is either a Microsoft exit code (if the app is uninstalled via Windows Installer) or it is unique to the application uninstaller (in which case you need to contact the vendor to find out what exit code 1605 means).
Assuming that the app being uninstalled via SCCM uses Windows Installer, an exit code of 1605 means:
This action is only valid for products that are currently installed.
If you get this error while installing an application through SCCM, then you may have an uninstaller as a dependancy that is trying to uninstall a program that isn’t installed. A dependancy failure with exit code 1605 will cause the installation to fail to proceed to the install stage.