My guess is that add-on system decides that your add-on cannot be installed and that's why you don't see it in the UI. However, the same verification should be performed when you install the add-on using manual upload. So it sounds a bit strange if you can install the same packages manualy.

Could you enable the logging with debug level for add-on system and see how the system loads and verifies the packages? Add something like this in EPiServerLogging.config:

<?xml version="1.0" encoding="utf-8"?>
<log4net>
...

<appender name="outputDebugStringAppender" type="log4net.Appender.OutputDebugStringAppender" >
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="[%thread] %level %logger: %message%n" />
</layout>
</appender> 

<logger name="EPiServer.Packaging" additivity="false">
<level value="Debug" />
<appender-ref ref="outputDebugStringAppender" />
</logger>

... 
</log4net>

Here I use DebugView tool, but you can log it to the file.

Hi!

Sees like I had not verified that the package was installable. 

When I fixed the .net45 bug, everything worked as intended.

(earlier I teseted with a package generated manually on my locale machine and not on the build server)

Thanks

ErikM