The interaction between inner and outer layer in large-eddy simulations that use approximate boundary conditions is studied. In hybrid R.ANS/LES models a transition layer exists between the RANS and LES regions, that may result in incorrect prediction of the velocity profiles, and errors of up to 15% in the prediction of the skin friction. Several factors affect this transition layer. In general, it is found that the correct prediction of length- and time-scales of the turbulent eddies in the RANS region is important in ensuring correct results, but is not the only factor affecting the results. Modeling errors in the LES region also affect the mean velocity profiles.