Getting Error code '0x801882CB' for Signed internal Appx while using InstallationManager.AddPackageAsync(appTitle, appUri)

I have developed WP8 Company App that manages internal signed apps. I am using InstallationManager.AddPackageAsync(appTitle, appUri) to download and install apps to the phone.

My device is a Lumia 1520 with 8.10.12382.878 OS.

Apps (.XAP) signed with C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v8.0\Tools\MDILXAPCompile\BuildMDILXap.ps1 installs fine.

New app (.APPX) signed with C:\Program Files (x86)\Microsoft SDKs\WindowsPhoneApp\v8.1\Tools\MDILXAPCompile\BuildMDILAPPX.ps1 fails with "Exception from HRESULT: 0x801882CB"

Why do I get "Exception from HRESULT: 0x801882CB"?

EDIT: It turns out that the MIME type (.APPX) was not allowed in IIS.

I added appx and appxbundle with MIME Type "application/octet-stream" and the installation got further but the installation still fails. New error: "Please contact your software vendor. (Exception from HRESULT: 0x80073CF9)".