Hi Sebastian,
You can definitely use tracing from WinClient applications. That unfortunate exception is due to a kind of race condition at startup -- TraceFns.WriteLine needs the TraceFns static class initialized, which in turn needs the IdeaBladeConfig.Instance loaded. We're not correctly detecting this, or controlling initialization sequence, so you get this ugly error.
There's an easy workaround, however, and is what we actually do automatically in the server-side code (for slightly different reasons) -- just call the following before the TraceFns.WriteLine call:
IdeaBlade.Core.IdeaBladeConfig.AssertNonDefaultVersion();
This will ensure that the IdeaBladeConfig is initialized, and you can then use TraceFns normally.