I have used this protocol several times but it is a very tedious process and takes a long time for the MSCs to grow and proliferate. I now use another protocol of isolating the cells from compact bone of mouse (Zhu et al, Nature protocols). This is a straight forward protocol giving me a very high yield of MSCs. If you need I can help you with this protocol.
Also to add I have emailed the authors of the paper you are referring to (Soliemani et al) several times as there are many discrepancies in their protocol and their previously published paper which was the basis of this protocol. They have never replied to me as well as the editor of Nature protocols (I contacted them too).