Cryptographic schemes are usually computed over finite fields or rings in order to protect the user's privacy, because of computations over finite fields or rings are not order-keeping, which are useful to obscure and dissipate the redundancies in a plaintext message. Recently, Lei et al. proposed two schemes [IEEE Transaction on Cloud Computing, 78-87 (2013), Information Sciences, 205-217 (2014)] for outsourcing matrix inversion computation and matrix multiplication computation to the cloud. All computations in the schemes are computed over the infinite field R. In this paper, we would like to stress that both two schemes are awed because the computational errors are not considered at all. The proposed verifying equations do not hold. We will analyze the involved rounding errors and revise the original checking mechanisms. We think it is helpful to reinforce the differences between the arithmetic over R and that over any finite fields or rings.