i guess that's most likely because you press a button or something in your form and then you create there the entity, but this leads almost inevitably to problems, as functions may only be called when the engine is no in the engine_frame or any other engine function ^^
thus the proper way to create an entity or interact with the entity from another thread - thus in the function of your button is the following (like in the example on the homepage) - should be
Code:
private void changeTextButton_Click(object sender, EventArgs e)
{
    //add this function THREAD SAFE to the scheduler
    Scheduler.AddEventVoidThreadSafe(createEntity);
}
static ENTITY dummy = null;
private IEnumerable changeText()
{
    dummy = ENTITY.ent_create("some entity", new Vector(), null);
    yield return 1;
}


if this doesn't work for you - send me the part of your project or a small example project were this happens and I'll have a look at it !


get the C# wrapper:
for A7.85.4 and A8.30.4, Version 2.3.9
at http://acknexwrapper2.matthias-auer.net/ or visit the thread