Symptoms

The Android K2 Task List app is not working. The customer is using HTTP only.
 

Diagnoses

We made sure the bindings are correct in IIS and switched off HTTPS in the web.config by following this KB:
https://www.k2.com/onlinehelp/k2blackpearl/devref/4.6.9/default.htm_configure_non-ssl_(development_only).html

Then we made sure the bindings are correct further down in the web.config for K2WebServices.

After this it was still not working, even when the customer turned on SSL in IIS as a test. They were getting an error "java.lang.IllegalStateException: Scheme HTTP not registered".
 

Resolution

We finally figured out that the Android devices use a Proxy server to connect to the K2 server, after switching off the proxy and connecting directly, it seems to work now. However this is unfortunately just a workaround and a Product Feature Enhancement Request has been logged.

The new Android version of K2 Mobile should release in the next few months that uses the newer K2API interface (instead of the older K2WebServices that the K2 Task List app uses). I'm sure that the developers will take this issue into consideration during development of the new app.