There are usually two causes for this issue.
- You are invoking your caller before the proxy provider is initialized.
- You have added a new endpoint, but SDM has not rerun the Errai proxy generator.
You can fix (1) by making sure your endpoint is called in an @AfterInitialization method. But if you only see the problem in dev mode, it's more likely that (2) is your issue.
You can fix (2) by either cleaning your SDM cache, or touching (i.e. modifying the timestamp on the file) of an existing RPC interface that you know is working.
Restarting whole pc helped. I've notice this to happend offen after suspending pc.