Robustness is one of the most important issues in digital watermarking. By modeling digital watermarking as digital communications, several researchers proposed using error correcting coding (ECC) to improve watermark robustness. However, the following important facts are neglected. i) The robust watermark channel suffers from a very high bit error ratio (BER), which may exceed the capability of ECC; ii) Due to the imperceptibility requirement, the redundancy introduced by ECC will lead to a decrease of the watermark magnitude. Could the usage of ECC effectively improve the robustness of watermark? This paper addresses this problem from the perspectives of both theoretical analysis and experiments. Our investigation shows that ECC cannot effectively improve the robustness of watermarking against a vast majority of various attacks except for cropping and jitter attacks. Hence, ECC should not be considered as a universal method applied to enhance the watermark robustness.