Found a mistake in a proof about when GGH will decrypt incorrectly The proof is here on page 66, lemma 20. I found the same mistake in other sources also.

It claims that GGH decryption will fail only if $\lceil R^{-1}e\rfloor \not =0$. Here $R$ is the "good" private basis for the lattice and $e$ is the small random vector. Rounding symbol means just that every coordinate of the vector will be rounded to the nearest integer.

In the proof they use the "fact" that $B^{-1}R$ is an unimodular matrix. They come to this conclusion from the fact that the two bases are connected by a unimodular matrix $U$ like this

$$B=UR.$$

This is correct. However from this they deduce that $$U^{-1}=B^{-1}R.$$ This is clearly false. Actually $$U^{-1}=RB^{-1}.$$ There is no guarantee that $B^{-1}R$ is unimodular.

Have any of you come across another way to prove this result?
Okay, this was a really stupid mistake by me. I got confused because some sources use notation where $R$ and $B$ have the basis vectors as rows. However Goldreich, Goldwasser and Halevi have the basis vectors as columns so 
$$B=RU\implies U=R^{-1}B.$$ Hence the matrix is unimodular and the proof works. Sorry about the inconvience.