Dielectric waveguides are a potential platform for future integrated THz electronics but are still challenging to interface with standard measurement equipment. The commonly used tapered transition to hollow metallic waveguides involves manual alignment, leading to measurement inaccuracies. In this paper, we report the effects of misalignment between a dielectric and a metallic waveguide in the W-band. The results indicate the excitation of unwanted high-order modes in the dielectric waveguide that are expected to degrade the performance, especially at higher frequencies.