if something will be changed if you change the inplaceSelect to h:selectOneMenu?
B.t.w. probably you trying to use your custom objects instead of selectItems for select without proper converter for them.
I have tried using h:selectOneMenu also but still I am having the same problem. Validation error value is not valid.
This means there's a problem in your application code. Check that equals()/hashCode() are correctly implemented, then try to add converter if none exists.