What that error means is that there were no @Remote interfaces found and no proxies registered when the first RPC was attempted. The reason for this could be that your kitschensink-shared project does not have an ErraiApp.properties file. That file is required so that the classes in this module get scanned by Errai.
Thank you very much for answer. I appreciate the prompt help! It solved my issue
The kitchensink-shared project didn't have an ErraiApp.properties files. I was aware of this necessity in general but I thought that it is enough when the kitchensink-client project has one...