It may be more accurate to say that Hayek thought Mises misunderstood the reason why central planners can’t calculate in socialism. Peter Klein, an expert on Hayek, makes some relevant comments in this article:
http://mises.org/page/1454/Biography-of-F-A-Hayek-18991992
Here is Mises on Hayek’s contribution to the economic calculation debate:
http://mises.org/journals/qjae/pdf/qjae3_1_2.pdf
